Antimicrobial nonwoven polyamides with zinc content

ABSTRACT

The present disclosure relates to a nonwoven polyamide structure having antimicrobial properties comprising: nonwoven polyamide fibers comprising less than 4000 ppm zinc dispersed within the nonwoven polyamide fibers; and less than 2000 ppm phosphorus. The fibers have an average fiber diameter of less than 25 microns; and the polyamide structure demonstrates a Staphylococcus Aureus reduction of at least 90%, as measured by ISO 20743-13.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority to U.S. ProvisionalPatent Application No. 62/781,233 filed Dec. 18, 2018, which isincorporated herein by reference.

FIELD

The present disclosure relates to nonwoven polyamides having permanentantimicrobial properties. In particular, the present disclosure relatesto antimicrobial nonwoven polyamides comprising unique antimicrobialcomponent(s).

BACKGROUND

There is a growing interest in fabrics having antimicrobial properties.In some instances, a number of treatments or coatings are applied tofibers to impart antimicrobial properties to fabrics. Compoundscontaining copper, silver, gold, or zinc, either individually or incombination, have been used in these applications to effectively combatpathogens such as bacteria, mold, mildew, virus, spores, and fungus.

These types of antimicrobial fibers and fabrics may be used in manyindustries including healthcare, hospitality, military, and athletics,among others. However, conventional antimicrobial fibers and fabricshave difficulties in meeting many of the other requirements of theseapplications. Additionally, many purported antimicrobial fabrics do nothave sufficient antimicrobial properties, nor do they retain theseproperties for the lifetime of the product in which they are utilized.In some instances, the antimicrobial additives may have adverseenvironmental consequences by leaching from the fabric.

For example, in the healthcare and hospitality industries, certainfabrics are required to be sanitary at all times. To comply with thesesanitation standards, the fabrics are subject to daily washing and,often times, bleaching. As another example, athletic wear is susceptibleto bacterial growth due to both internal and external factors, and sweatand bacteria transmitted through the skin can lead to the growth ofbacteria in clothing fibers. In some cases, these bacteria lead tounpleasant odors, staining, fabric deterioration, and even physicalirritation, such as skin allergies and skin infections. Thus, in manyapplications repeated cycles of use and washing are quite common.Unfortunately, conventional fabrics have been found to deteriorate andlose antimicrobial properties during repeated uses and/or wash cycles.

As one example of conventional antimicrobial yarns and fabrics, U.S.Pat. No. 6,584,668 discloses durable non-electrically conductive metaltreatments applied to yarns and textile fabrics. The durablenon-electrically conductive metal treatments are coatings or finishesapplied to yarns and textile fabrics. The metal treatments may includesilver and/or silver ions, zinc, iron, copper, nickel, cobalt, aluminum,gold, manganese, magnesium, and the like. The metal treatments areapplied to the exterior surface of the yarn or fabric as a coating orfilm.

In addition, U.S. Pat. No. 4,701,518 discloses an antimicrobial nylonprepared in water with a zinc compound (ZnO) and phosphorus compound toform carpet fibers. The process produces nylon fibers for carpets having18 denier per filament (dpf), and are prepared by conventional meltpolymerization. Such carpet fibers typically have average diameters thatare well above 30 microns, which are generally unsuitable fornext-to-skin applications.

Conventional polymer formulations, e.g., the aforementioned nylonformulations, have been known to be difficult to process, especially incases where smaller fibers (and lower denier) are desired, e.g., innonwoven applications. For example, the conventional formulations thatcomprise, for example, nylon and various other additives, may requirehigher die pressures to form the smaller diameter fibers, which may, inturn, lead to detrimental fiber interruptions. In some cases, typicalpolymer formulations have relative viscosities that are too high toeffectively process and may require adjustment, which may reduce overallefficiency.

Although some references may teach the use of antimicrobial fibers andfabrics, a need still exists for antimicrobial fibers and fabrics thatretain their antimicrobial properties after multiple washes, whilemaintaining fiber strength and still being efficient to process, e.g.,having lower relative viscosities and/or using lower die pressures.

SUMMARY

According to some embodiments, the present disclosure relates to anonwoven polyamide composition having permanent antimicrobial propertiescomprising: a nonwoven polyamide having an average fiber diameter ofless than 25 microns; less than 2000 ppm of zinc dispersed within thenonwoven polyamide; and less than 2000 ppm of phosphorus; wherein theweight ratio of the zinc to the phosphorus is: at least 1.3:1; or lessthan 0.64:1. In some aspects, the weight ratio of the zinc to thephosphorus is at least 2:1. The relative viscosity of the polyamidecomposition may range from 10 to 100, e.g., from 20 to 100. In someaspects, the polyamide composition may comprise less than 500 ppm ofzinc. The polyamide composition may comprise a delusterant including atleast a portion of the phosphorus. In some aspects, the polyamidecomposition comprises no phosphorus. The zinc may be provided via a zinccompound comprising zinc oxide, zinc acetate, zinc ammonium carbonate,zinc ammonium adipate, zinc stearate, zinc phenyl phosphinic acid, zincpyrithione and/or combinations thereof. In some aspects, the zinccompound does not comprise zinc phenyl phosphinate and/or zinc phenylphosphonate. In some aspects, the phosphorus is provided via aphosphorus compound comprising phosphoric acid, benzene phosphinic acid,benzene phosphonic acid, manganese hypophosphite, sodium hypophosphite,monosodium phosphate, hypophosphorous acid, phosphorous acid, and/orcombinations thereof. In some aspects, the polyamide compositioncomprises less than 500 ppm of zinc, wherein the polyamide compositioncomprises a delusterant including at least a portion of the phosphorus,and wherein the polyamide composition demonstrates a StaphylococcusAureus reduction of at least 90%, as measured by ISO 20743-13. In someaspects, the polyamide comprises a nylon, wherein the zinc is providedvia zinc oxide and/or zinc pyrithione, and wherein the relativeviscosity of the polyamide composition ranges from 10 to 100, e.g., from20 to 100. In some aspects, the polyamide comprises nylon-6,6, whereinthe zinc is provided via zinc oxide, wherein the weight ratio of zinc tophosphorus is at least 2:1, and wherein the polyamide compositiondemonstrates a Staphylococcus Aureus reduction of at least 90%, asmeasured by ISO 20743-13. The nonwoven may further comprise one or moreadditional antimicrobial agents comprising silver, tin, copper, andgold, and alloys, oxides, and/or combinations thereof. The melt point ofthe nonwoven may be 225° C. or greater. The nonwoven polyamide may beformed by melt, solution, centrifugal, or electro-spinning. In someaspects, the average fiber diameter of the nonwoven polyamide is 1000nanometers or less. In some aspects, no more than 20% of the fibers havea diameter of greater than 700 nanometers. In some aspects, thepolyamide comprises nylon 66 or nylon 6/66. In some aspects, thepolyamide comprises a high temperature nylon. In some aspects, thepolyamide comprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T,N11, and/or N12, wherein “N” means Nylon. In some aspects, the nonwovenpolyamide has an Air Permeability Value of less than 600 CFM/ft². Insome aspects, the nonwoven polyamide has a basis weight of 200 GSM orless.

In some embodiments, the disclosure relates to nonwoven polyamide, e.g.,nylon 66 or nylon 6/66, structure having antimicrobial propertiescomprising: nonwoven polyamide fibers comprising less than 4000 ppmzinc, e.g., less than 3200 ppm, or less than 3100 ppm, dispersed withinthe nonwoven polyamide fibers; and less than 2000 ppm phosphorus. Thefibers have an average fiber diameter of less than 25 microns, e.g.,less than 20 microns. The polyamide structure demonstrates aStaphylococcus Aureus reduction of at least 90%, as measured by ISO20743-13. The weight ratio of the zinc to the phosphorus may be at least1.3:1; or less than 0.64:1. The relative viscosity of the polyamidecomposition may be less than 100. The structure and/or the fibers maycomprise a delusterant including at least a portion of the phosphorus.The nonwoven polyamide may be melt spun, spunbonded, electrospun,solution spun, or centrifugally spun. In some cases, no more than 20% ofthe fibers have a diameter of greater than 700 nanometers. Theantimicrobial fibers may have a zinc retention greater than 70% asmeasured by a dye bath test.

In some embodiments, the disclosure relates to a process for preparingan antimicrobial nonwoven polyamide structure having permanentantimicrobial properties, the process comprising: preparing precursorpolyamide optionally comprising an aqueous monomer solution; dispersingless than 4000 ppm zinc within the precursor polyamide; dispersing lessthan 2000 ppm phosphorus within the precursor polyamide; polymerizingthe precursor polyamide to form a polyamide composition; spinning thepolyamide composition to form antimicrobial polyamide fibers; andforming the antimicrobial polyamide fibers into the antimicrobialnonwoven structure having a fiber diameter of less than 25 microns. Theantimicrobial fibers may have a zinc retention greater than 70% asmeasured by a dye bath test. The weight ratio of the zinc to thephosphorus may be at least 1.3:1; or less than 0.64:1. The polyamide maybe melt spun by way of melt blowing through a die into a high velocitygaseous stream. The nonwoven polyamide may be melt spun, spunbonded,electrospun, solution spun, or centrifugally spun. The nonwoven maycomprises a nylon 66 polyamide which is melt spun into fibers and formedinto said nonwoven, wherein no more than 20% of the fibers have adiameter of greater than 25 microns.

According to some embodiments, the present disclosure relates toantimicrobial fibers having permanent antimicrobial propertiescomprising: a nonwoven polyamide having an average fiber diameter ofless than 25 microns; less than 2000 ppm of zinc dispersed within thenonwoven polyamide; and less than 2000 ppm of phosphorus. In someaspects, the weight ratio of zinc to phosphorus is: at least 1.3:1; orless than 0.64:1. In some aspects, the weight ratio of the zinc to thephosphorus is at least 2:1. In some aspects, the fibers have an averagediameter less than 20 microns. The nonwoven polyamide may comprise lessthan 500 ppm of zinc. The nonwoven polyamide may comprise a delusterantincluding at least a portion of the phosphorus. The antimicrobial fibersmay have a zinc retention greater than 70% as measured by a dye bathtest. The zinc may be a zinc compound comprising zinc oxide, zincacetate, zinc ammonium carbonate, zinc ammonium adipate, zinc stearate,zinc phenyl phosphinic acid, zinc pyrithione and/or combinationsthereof. The phosphorus may be a phosphorus compound comprisingphosphoric acid, benzene phosphinic acid, benzene phosphonic acid,manganese hypophosphite, sodium hypophosphite, monosodium phosphate,hypophosphorous acid, phosphorous acid, and/or combinations thereof. Thenonwoven polyamide may comprise less than 500 ppm of zinc, wherein thepolymer comprises a delusterant including at least a portion of thephosphorus, and wherein the antimicrobial fibers demonstrates aStaphylococcus Aureus reduction of at least 90%, as measured by ISO20743-13. The nonwoven polyamide may comprises nylon, wherein the zincis provided in the form of zinc oxide and/or zinc pyrithione, whereinthe relative viscosity of the polymer resin composition ranges from 10to 100, e.g., from 20 to 100, and wherein the antimicrobial fibers havea zinc retention greater than 80% as measured by a dye bath test, andwherein the fibers have an average diameter less than 18 microns. Thenonwoven polyamide may comprise nylon-6,6, wherein the zinc is providedin the form of zinc oxide, wherein the weight ratio of zinc tophosphorus is at least 2:1, wherein the antimicrobial fibers demonstratea Staphylococcus Aureus reduction of at least 90%, as measured by ISO20743-13, wherein the antimicrobial fibers have a zinc retention greaterthan 95% as measured by a dye bath test, and wherein the antimicrobialfibers have an average diameter less than 10 microns. The nonwovenpolyamide may further comprise one or more additional antimicrobialagents comprising silver, tin, copper, and gold, and alloys, oxides,and/or combinations thereof. The melt point of the nonwoven may be 225°C. or greater. The nonwoven polyamide may be melt spun, spunbonded,electrospun, solution spun, or centrifugally spun. In some aspects, theaverage fiber diameter of the nonwoven polyamide may be 1000 nanometersor less. In some aspects, no more than 20% of the fibers have a diameterof greater than 700 nanometers. The polyamide may comprise nylon 66 ornylon 6/66. The polyamide may comprise a high temperature nylon. Thepolyamide may comprise N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T,N11, and/or N12, wherein “N” means Nylon. The nonwoven polyamide mayhave an Air Permeability Value of less than 600 CFM/ft². The nonwovenpolyamide may have a basis weight of 200 GSM or less. Basis weight maybe determined by ASTM D-3776 and reported in GSM (g/m²).

According to some embodiments, the present disclosure relates to aprocess for preparing antimicrobial nonwoven polyamides having permanentantimicrobial properties, the process comprising: preparing an aqueousmonomer solution for forming a polyamide; adding less than 1000 ppm ofzinc dispersed within the aqueous monomer solution; adding less than2000 ppm of phosphorus; polymerizing the aqueous monomer solution toform the polyamide; spinning the polyamide to form the antimicrobialpolyamide fibers; and forming the antimicrobial polyamide fibers intoantimicrobial nonwoven polyamides having a fiber diameter of less than25 microns; wherein the weight ratio of zinc to phosphorus is: at least1.3:1 or less than 0.64:1. The polyamide may comprise less than 2000 ppmzinc. The antimicrobial fibers may have a zinc retention greater than70% as measured by a dye bath test. The step of adding phosphorus maycomprise adding a delusterant including at least a portion of thephosphorus. The polyamide may be melt spun by way of melt blowingthrough a die into a high velocity gaseous stream. The polyamide may bemelt spun by 2-phase propellant-gas spinning, including extruding thepolyamide composition in liquid form with pressurized gas through afiber-forming channel. The nonwoven may be formed by collecting thefibers on a moving belt. In some aspects, the relative viscosity of thepolyamide in the nonwoven may be reduced as compared to the polyamideprior to spinning and forming the nonwoven. In some aspects, therelative viscosity of the polyamide in the nonwoven is the same orincreased as compared to the polyamide prior to spinning and forming thenonwoven. The nonwoven may comprise a nylon 66 polyamide which is meltspun and formed into said nonwoven, wherein the nonwoven has a TDI of atleast 20 ppm and an ODI of at least 1 ppm. The nonwoven may comprise anylon 66 polyamide which is melt spun into fibers and formed into saidnonwoven, wherein no more than 20% of the fibers have a diameter ofgreater than 25 microns. In some aspects, the polyamide is melt spun,spunbonded, electrospun, solution spun, or centrifugally spun.

In some embodiments, the disclosure relates to a nonwoven polyamidestructure having antimicrobial properties comprising: nonwoven polyamidefibers having an average fiber diameter of less than 25 microns; lessthan 4000 ppm zinc dispersed within the nonwoven polyamide fibers. Thepolyamide composition may demonstrate a Staphylococcus Aureus reductionof at least 90%, as measured by ISO 20743-13.

In some embodiments, the disclosure relates to a process for preparingan antimicrobial nonwoven polyamide structure having antimicrobialproperties, the process comprising: preparing a formulation comprising apolyamide, less than 4000 ppm zinc dispersed within the polyamide; andless than 2000 ppm phosphorus dispersed within the polyamide; spinningthe formulation to form antimicrobial polyamide fibers having a fiberdiameter of less than 25 microns; and forming the antimicrobialpolyamide fibers into antimicrobial nonwoven polyamide structure. Thefibers may be spun using a die pressure less than 275 psig.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure is described in detail below with reference to thedrawings wherein like numerals designate similar parts and wherein:

FIG. 1 and FIG. 2 are separate schematic diagrams of a 2-phasepropellant-gas spinning system useful in connection with the presentdisclosure;

FIG. 3 is a photomicrograph of a nanofiber nylon 66 melt spun into anonwoven having an RV of 7.3 at a magnification of 50×; and

FIG. 4 is a photomicrograph of a nanofiber of a grade from FIG. 3 ofnylon 66 melt spun into a nonwoven having an RV of 7.3 at amagnification of 8000×; and

FIG. 5 is a schematic diagram of a melt blowing method in connectionwith embodiments of the present disclosure.

FIG. 6 is a photomicrograph of a nanofiber of nylon 66 with an RV of 36at a magnification of 100×.

FIG. 7 is a graph comparing thermal degradation index and oxidativedegradation index values for nanofiber samples as a function of dietemperature.

FIG. 8 is a graph comparing thermal degradation index and oxidativedegradation index values for nanofiber samples as a function of meterpump speed.

DETAILED DESCRIPTION

Introduction

As discussed above, some conventional antimicrobial fibers and fabricsutilize antimicrobial compounds to inhibit pathogens. For example, somefabrics may include antimicrobial additives, e.g., silver, applied as afilm on an exterior layer via a topical treatment. It has been found,however, that these treatments often (quickly) leach from the fabric.Likewise, in some non-coating applications where the antimicrobialadditives are a component of the fiber, the antimicrobial additives havealso been known to wash out, usually within about 10 wash-cycles,leaching the additives into the environment.

The disclosed nonwoven fibers and fabrics, however, advantageouslyeliminate the need for a topical treatment to make apparelantimicrobial. The present antimicrobial fibers and fabrics have“built-in” antimicrobial properties. And these properties beneficiallywill not wash away after significant washing or wash cycles. Further,the antimicrobial fibers can maintain colorfastness (a characteristicthat relates to a material's resistance to color fading or running) anddurability. Unlike conventional antimicrobial fabrics, the presentfibers and fabrics do not lose their antimicrobial activity fromleaching and extraction after repeated use and wash cycles.

Also, the references that relate to carpet fibers relate to higherdenier (for example, greater than 12 dpf) and/or higher fiber diameter(for example, greater than 20 microns) fibers/filaments. These carpetfibers are formed via entirely different, non-analogousprocesses/equipment (filament spinning vs. fiber blowing), which resultsin entirely different products (a single, longer, thicker filament vs. aplurality of thinner intertwined fibers). In view of these significantdifferences, the teachings of such carpet fiber references are nottypically considered relevant to blowing operations, e.g., nonwovens.More specifically, in carpet fiber production, formulations havingdifferent amounts, e.g., higher amounts, of phosphorus compounds(optionally with zinc compounds) are employed for their ability toincrease relative viscosity of the polymer.

However, phosphorous compounds are not typically used in non-carpet,e.g., textile, polymer formulations because the use and the accompanyingrelative viscosity build might contribute to processability issues.Stated another way, the nonwoven equipment and processes cannot processthe carpet formulation (with the increased relative viscosity), becauseit could impede processability and make production difficult if notimpossible. In contrast to carpet formulations, the (nonwoven) polyamidecompositions disclosed herein comprise a unique combination of zinc andoptionally phosphorus, each preferably in particular amount, e.g., loweramounts, that retards or eliminates the viscosity build that isassociated with conventional carpet fiber formulations (and alsoprovides additional synergistic benefits). As a result, the nonwovenformulations disclosed herein are surprisingly capable of forming muchthinner fibers having antimicrobial properties, e.g., in the form of anonwoven web, without the aforementioned processing problems.Conventional formulations could not be effectively spun into such thindiameter fibers, e.g., nanofiber nonwoven webs.

Still further, conventional nylon formulations that employ antimicrobialagents may require the use of higher die pressures to form the smallerdiameter fibers of nonwoven mats. These higher die pressures often leadto higher detrimental fiber interruptions.

Also, although some references directly mix antimicrobial agents withfibers, leathers, or plastics, such processes did not solve problems ofquality deterioration of products since the antimicrobial ability waslost due to heat degradation, loss of colorfastness, or problems due tothe elution of antimicrobial substances. Still other conventionalantimicrobial fabrics, e.g., nonwoven fabrics, have been found to haveinsufficient strength for apparel applications, e.g., an inability towithstand significant washing, and are unable to retain antimicrobialproperties over the product lifetime.

Further, it has now been discovered that presence of zinc (zinccompounds) and optionally phosphorus, each preferably in specificamounts in a nonwoven polyamide composition, is capable of providing foreffective production of antimicrobial nonwoven fibers, e.g., nanofibers,that are able to retain enduring antimicrobial properties. Theproduction of these fibers may be advantageously achieved using lowerdie pressure operation. In some cases, the compositions have lowerrelative viscosity (RV), which may contribute to the lower die pressureoperation. Without being bound by theory, in some embodiments, the useof the phosphorus compound in the specific amounts may allow the zinc tobe more stably disposed in the polymer and/or in the fibers, and, assuch, may retard leaching of the zinc from the fibers/fabrics, e.g.,during washing. Stated another way, the polyamide composition may havecertain amounts of zinc and phosphorus embedded in the polyamide suchthat they retain permanent antimicrobial properties. Additionally, theuse of a nonwoven polyamide as the polymer resin, especially a nonwovenpolyamide formed by a melt spinning, solution spinning, centrifugalspinning, or electro-spinning process, has been found to have improveddurability. There are numerous additional benefits to using a melt blownor spun nonwoven polyamide, as are described further herein.

It was also beneficially found that providing a zinc compound andoptionally a phosphorus compound to the polymer composition during theproduction process of the fibers, e.g., to the aqueous monomer solutionor via masterbatch, produces fibers with antimicrobial agents evenlydispersed throughout the entire fiber. In conventional processes, asilver coating is applied to the outer surface of the fabric to impartantimicrobial properties to the fabric. However, the silver coating isnot dispersed throughout the fabric and is more susceptible to leachingcomponents, e.g., silver, into the environment. Advantageously, thepresent polymer composition does not give rise to toxicity because itdoes not elute the antimicrobial agents, nor does it include any toxiccomponents, e.g., silver. Additionally, antimicrobial fibers formed thepresent polymer composition do not require a separate application stepsince the antimicrobial agents are permanently disposed in the polymerand/or in the fibers.

In other embodiments, the compositions comprise little or no phosphorus.The disclosed zinc compounds, optionally in the disclosed amounts, lendbeneficial properties to the antimicrobial polyamide composition and tothe processes that employ them, e.g., low die pressure operation.

As noted above, as an additional benefit, the fibers formed using thenonwoven polyamide formulation/composition, have advantageous physicalfeatures, e.g., lower average fiber diameter, which allows them to beused in various applications, where higher fiber diameter areunsuitable, e.g., apparel or other next-to-skin applications as well asfiltration, where the thicker fibers are unsuitable.

In one aspect, the present disclosure relates to a polyamideformulation/composition, which may in some cases be used to formantimicrobial fibers (nanofibers) optionally arranged to form thepolyamide structure. The nonwoven polyamide composition comprisesparticular antimicrobial agents, which are efficacious and aresignificantly resistant to washing or wearing from the fiber.Importantly, the formulations provide for processing advantages, forexample, the ability to form thinner diameter fibers, the ability to beused in low die pressure operation, and/or the ability have preferredrelative viscosity (RV) parameters. In one aspect, the antimicrobialfibers form fabrics or certain portions of fabrics. In some embodiments,the formulations comprise a polyamide or polyamide mixture and a zinccompound. In some cases, the formulations further comprise a phosphoruscompound. Details of the components (and the compositional amountsthereof), the items formed therefrom, and the performancecharacteristics thereof are disclosed herein.

In some embodiments, the disclosure relates to a nonwoven polyamidestructure, e.g., a mat, having antimicrobial properties. The structurecomprises thin diameter polyamide fibers (in some cases nonwovenfibers), e.g., having an average fiber diameter of less than 25 microns.The fibers comprise zinc compound in specific amounts, and the zinc isdispersed within the fibers (as a component of the fibers/polymer),which is in contrast to conventional fibers or structures that may havean antimicrobial coating on the surfaces thereof.

The structure (and/or the fibers that form the structure) demonstratesimproved antimicrobial performance, e.g. the structure demonstrates aStaphylococcus Aureus reduction of at least 90%, e.g., at least 99%, ora Klebsiella pneumonia reduction of at least 90% growth, e.g., at least99%, as measured by ISO 20743-13.

Antimicrobial Components

As noted above, the polyamide formulation includes zinc and optionallyphosphorus, preferably in specific amounts in the polyamide composition,which provide the aforementioned antimicrobial benefits and/orphysical/performance benefits. As used herein, “zinc compound” refers toa compound having at least one zinc molecule or ion. As used herein,“phosphorus compound” refers to a compound having at least onephosphorus molecule or ion.

The polyamide formulation (or the structures or fibers made therefrom)comprises (elemental) zinc, e.g., zinc is dispersed within the polyamideformulation. In some embodiments, the concentration of zinc in thepolyamide formulation is in a range from 100 ppb to 4000 ppm, e.g., from500 ppb to 3500 ppm, from 1 ppm to 3500 ppm, from 200 ppm to 3000 ppm,from 275 ppm to 3100 ppm, from 200 ppm to 1500 ppm, from 100 ppm to 2000ppm, from 200 ppm to 700 ppm, from 250 ppm to 550 ppm, from 1 ppm to1000 ppm, e.g., from 25 ppm to 950 ppm, from 50 ppm to 900 ppm, from 100ppm to 800 ppm, from 150 ppm to 700 ppm, from 175 ppm to 600 ppm, from200 ppm to 500 ppm, from 215 ppm to 400 ppm, from 225 ppm to 350 ppm, orfrom 250 ppm to 300 ppm. In terms of lower limits, the polyamideformulation comprises greater than 100 ppb zinc, e.g., greater than 500ppb, greater than 1 ppm, greater than 5 ppm, greater than 10 ppm,greater than 25 ppm, greater than 50 ppm, greater than 75 ppm, greaterthan 100 ppm, greater than 150 ppm, greater than 175 ppm, greater than200 ppm, greater than 215 ppm, greater than 225 ppm, greater than 250ppm, or greater than 275 ppm. In terms of upper limits, the polyamideformulation comprises less than 4000 ppm zinc, e.g., less than 3500 ppm,less than 3000 ppm, less than 3100 ppm, less than 2000 ppm, less than1500 ppm zinc, less than 1000 ppm zinc, less than 950 ppm, less than 900ppm, less than 800 ppm, less than 700 ppm, less than 600 ppm, less than550 ppm, less than 500 ppm, less than 400 ppm, or less than 300 ppm. Insome aspects, zinc is embedded in the polymer formed from the polyamideformulation.

The manner in which the zinc is provided to the polyamide formulationmay vary widely. Many techniques for providing zinc in the polyamideformulation are within the contemplation of this disclosure and will besuitable. As one example, the zinc compound may be added as a componentof the polyamide. In one embodiment, zinc compounds can be added as amasterbatch. The masterbatch may include a polyamide such as nylon 6 ornylon 6,6. In yet other embodiments, the zinc compound may be added bydusting powder onto the pellets. In yet another embodiment zinc can beadded (as a powder) onto the nylon 6,6 pellets and processed through atwin screw extruder to more evenly distribute the material through thepolymer, enhancing the uniformity of the additive throughout the fabric.In one embodiment, the zinc compound may added to the salt solutionduring polyamide formation.

In some embodiments, the formulations, structures, and/or fiberscomprise (elemental) phosphorus. Regardless of how the phosphorus isprovided (see discussion below), the phosphorus, like the zinc, ispresent in the polyamide formulation. In some embodiments, theconcentration of phosphorus in the polyamide formulation ranges from 10ppm to 1000 ppm, e.g., from 20 ppm to 950 ppm, from 30 to 900, from 50ppm to 850 ppm, from 100 ppm 800 ppm, from 150 ppm to 750 ppm, from 200ppm to 600 ppm, from 250 ppm to 550 ppm, from 300 ppm to 500 ppm, orfrom 350 ppm to 450 ppm. In terms of upper limits, the concentration ofphosphorus in the polyamide formulation may be less than 1000 ppm, e.g.,less than 950 ppm, less than 900 ppm, less than 800 ppm, less than 700ppm, less than 600 ppm, less than 500 ppm, less than 400 ppm, less than300 ppm, or less than 200 ppm. In terms of lower limits, theconcentration of phosphorus in the polyamide formulation may be greaterthan 10 ppm, e.g., greater than 20 ppm, greater than 40 ppm, greaterthan 60 ppm, greater than 80 ppm, greater than 100 ppm, greater than 150ppm, or greater than 180 ppm. In some aspects, phosphorus is embedded inthe polymer of the polyamide formulation.

The manner in which the phosphorus is provided to the polyamideformulation may vary widely. Many techniques for providing phosphorus inthe polyamide formulation are within the contemplation of thisdisclosure and will be suitable. As one example, phosphorus or aphosphorus compound may be added as a component of the resin, e.g., inmanners similar to those of the zinc.

In one embodiment, the phosphorus may be provided as a component ofanother additive. For example, the phosphorus may be a component of adelusterant that is added to the polymer composition. Specifically, thephosphorus may be a coating additive/component of the delusterant. Insome aspects, the delusterant comprises titanium dioxide. The titaniumdioxide may comprise a phosphorus-containing surface coating, e.g.,manganese coated titanium dioxide. In some aspects, the phosphoruspresent in the polyamide composition is entirely supplied by theadditive, e.g., delusterant. In some aspects, the phosphorus present inthe polyamide composition is partly supplied by the additive and partlyas a phosphorus additive.

In some aspects, the phosphorus present in the polyamide formulation isentirely supplied by the delusterant, e.g., titanium dioxide additive,and no phosphorus, e.g., phosphorus additive, is separately added to thepolyamide composition. For example, the titanium dioxide additive may bepresent in the polymer formulation, wherein the titanium dioxideincludes less than 2000 ppm phosphorus based on the total weight of thepolyamide formulation. In some embodiments, the polyamide formulationmay include a titanium dioxide additive and a phosphorus additive, whichin conjunction, supply less than 2000 ppm of phosphorus based on thetotal weight of the polyamide formulation.

In some embodiments, inorganic pigment-like materials can be utilized asdelusterants. The delusterants may comprise one or more of titaniumdioxide, barium sulfate, barium titanate, zinc titanate, magnesiumtitanate, calcium titanate, zinc oxide, zinc sulfide, lithopone,zirconium dioxide, calcium sulfate, barium sulfate, aluminum oxide,thorium oxide, magnesium oxide, silicon dioxide, talc, mica, and thelike. Colored materials such as carbon black, copper phthalocyaninepigment, lead chromate, iron oxide, chromium oxide, and ultramarine bluemay also be used. In some aspects, the delusterants comprisenon-phenolic polynuclear compounds such as triphenyl benzene, diphenyl,substituted diphenyls, substituted naphthalenes, and chlorinatedcompounds of the aromatic and polynuclear type, e.g., chlorinateddiphenyl.

The inventors have found that, in some cases, the use of specific weightratios of zinc to phosphorus minimizes the negative effects of thephosphorus on the polyamide formulation. For example, too muchphosphorus in the polyamide composition can lead to polymer drip,increased polymer viscosity, and inefficiencies in production processes.

In one embodiment, the weight ratio of zinc to phosphorus in thepolyamide formulation may be greater than 1.3:1, e.g., greater than1.4:1, greater than 1.5:1, greater than 1.6:1, greater than 1.7:1,greater than 1.8:1, or greater than 2:1. In terms of ranges, the weightratio of zinc to phosphorus in the polyamide formulation may range from1.3:1 to 30:1, e.g., from 1.4:1 to 25:1, from 1.5:1 to 20:1, from 1.6:1to 15:1, from 1.8:1 to 10:1, from 2:1 to 8:1, from 3:1 to 7:1, or from4:1 to 6:1. In terms of upper limits, the weight ratio of zinc tophosphorus in the polyamide composition may be less than 30:1, e.g.,less than 28:1, less than 26:1, less than 24:1, less than 22:1, lessthan 20:1, or less than 15:1. In some aspects, there is no phosphorus inthe polyamide formulation. In other aspects, a very low amount ofphosphorus is present. In some cases, phosphorus is held in thefibers/polymer along with zinc.

In one embodiment, the weight ratio of zinc to phosphorus in thepolyamide formulation may be less than 0.64:1, e.g., less than 0.62:1,less than 0.6:1, e.g., less than 0.5:1, less than 0.45:1, less than0.4:1, less than 0.3:1, or less than 0.25:1. In terms of ranges, theweight ratio of zinc to phosphorus in the polyamide formulation mayrange from 0.001:1 to 0.64:1, e.g., from 0.01:1 to 0.6:1, from 0.05:1 to0.5:1, from 0.1:1 to 0.45:1, from 0.2:1 to 0.4:1, from 0.25:1 to 0.35:1,or from 0.2:1 to 0.3:1. In terms of lower limits, the weight ratio ofzinc to phosphorus in the polyamide formulation may be greater than0.001:1, e.g., greater than 0.005:1, greater than 0.01:1, greater than0.05:1, greater than 0.1:1, greater than 0.15:1, or greater than 0.2:1.

In some cases, it has been determined that a specific amount of zinc andphosphorus can be mixed in a polyamide formulation, e.g., polyamideresin composition, in finely divided form, such as in the form ofgranules, flakes and the like, to provide a polyamide formulation thatcan be subsequently formed, e.g., extruded or otherwise drawn, intofibers by conventional methods to produce fibers having substantiallyimproved antimicrobial activity. The zinc and phosphorus are employed inthe polyamide formulation in the aforementioned amounts to provide afiber with permanent antimicrobial activity.

As noted herein, by utilizing a polyamide formulation having theaforementioned zinc concentration, phosphorus concentration, andoptionally the range of relative viscosity and or other characteristics,the resultant antimicrobial fiber is capable of retaining a higherpercentage of zinc. The resulting nonwovens have (permanent or enduring)antimicrobial properties.

In some embodiments, the antimicrobial fibers formed from the polyamideformulation have a zinc retention greater than 70% as measured by thedye bath test, e.g., greater than 75%, greater than 80%, greater than90%, greater than 95%, or greater than 99%. In terms of upper limits,the antimicrobial fiber has a zinc retention of less than 100%, e.g.,less than 99.9%, less than 98%, less than 95% or less than 90%. In termsof ranges, the antimicrobial fiber has a zinc retention in a range from70% to 100%, e.g., from 75% to 99.9%, from 80% to 99%, or from 90% to98%.

The zinc retention of fibers formed from the polyamide formulation maybe measured by a dye bath test according to the following standardprocedure. A sample is cleaned (all oils are removed) by a scourprocess. The scour process may employ a heated bath, e.g., conducted at71° C. for 15 minutes. A scouring solution comprising 0.25% on weight offiber (“owf”) of Sterox (723 Soap) nonionic surfactant and 0.25% owf ofTSP (trisodium phosphate) may be used. The samples were then rinsed withwater and then rinsed with cold water.

The cleaned samples may be tested according to a chemical dye levelprocedure. This procedure may employ placing them in a dye bathcomprising 1.0% owf of C.I. Acid Blue 45, 4.0% owf of MSP (monosodiumphosphate), and a sufficient % owf of disodium phosphate or TSP toachieve a pH of 6.0, with a 28:1 liquor to fiber ratio. For example, ifa pH of less than 6 is desired, a 10% solution of the desired acid maybe added using an eye dropper until the desired pH was achieved. The dyebath may be preset to bring the bath to a boil at 100° C. The samplesare placed in the bath for 1.5 hours. As one example, it may takeapproximately 30 minutes to reach boil and then hold the bath at a boilfor one hour. Then the samples are removed from the bath and rinsed. Thesamples are then transferred to a centrifuge for water extraction. Afterwater extraction, the samples were laid out to air dry. The componentamounts before and after the procedure are then measured and recorded.

In some embodiments, the zinc may be provided as a zinc compound. Thezinc compound may comprise zinc oxide, zinc acetate, zinc ammoniumcarbonate, zinc ammonium adipate, zinc stearate, zinc phenyl phosphinicacid, zinc pyrithione and combinations thereof. In some aspects, thezinc is provided in the form of zinc oxide. In some aspects, the zinc isnot provided via zinc phenyl phosphinate and/or zinc phenyl phosphonate.Beneficially, the inventors have found that these particular zinccompounds work particularly well because they readily disassociate toform more zinc ions.

In some embodiments, the phosphorus may be provided as a phosphoruscompound. In aspects, the phosphorus compound may comprisephenylphosphinic acid, diphenylphosphinic acid, sodiumphenylphosphinate, phosphorous acid, benzene phosphonic acid, calciumphenylphosphinate, potassium B-pentylphosphinate, methylphosphinic acid,manganese hypophosphite, sodium hypophosphite, monosodium phosphate,hypophosphorous acid, dimethylphosphinic acid, ethylphosphinic acid,diethylphosphinic acid, magnesium ethylphosphinate, triphenyl phosphite,diphenylrnethyl phosphite, dimethylphenyl phosphite, ethyldiphenylphosphite, phenylphosphonic acid, methylphosphonic acid, ethylphosphonicacid, potassium phenylphosphonate, sodium methylphosphonate, calciumethylphosphonate, and combinations thereof. In some embodiments, thephosphorus compound may comprise phosphoric acid, benzene phosphinicacid, benzene phosphonic acid, and combinations thereof. The phosphorusor phosphorus compound may also be dispersed in the polymer along withzinc.

In some embodiments, the antimicrobial agent, e.g., zinc, is added withphosphorus to promote the incorporation of the antimicrobial agent intothe fibers/polymer of the polyamide composition. This procedureadvantageously allows for more uniform dispersion of the antimicrobialagent throughout the eventual fiber. Further, this combination“builds-in” the antimicrobial within the polyamide composition to helpprevent or limit the active antimicrobial ingredients from being washedfrom the fiber.

In some embodiments, the polyamide composition may include additionalantimicrobial agents other than zinc. The additional antimicrobialagents may be any suitable antimicrobial, such as silver, copper, and/orgold in metallic forms, e.g., particulates, alloys and oxides, salts,e.g., sulfates, nitrates, acetates, citrates, and chlorides, and/or inionic forms. In some aspects, further additives, e.g., additionalantimicrobial agents, are added to the polyamide composition.

Antimicrobial Performance

In some embodiments, the formulation, structure, and/or fibersdemonstrate improved antimicrobial performance, e.g., after 24 hours.For example, the formulation, structure, and/or fibers may demonstrateStaphylococcus aureus reduction (inhibition of growth) of at least 90%,as measured by ISO 20743-13, e.g., at least 95%, at least 99%, at least99.98, at least 99.99, at least 99.997, at least 99.999, or at least99.9999.

In some embodiments, the formulation, structure, and/or fibersdemonstrate improved antimicrobial performance. For example, theformulation, structure, and/or fibers may demonstrate Klebsiellapneumoniae reduction (inhibition of growth) of at least 90%, as measuredby ISO 20743-13, e.g., at least 95%, at least 99%, at least 99.98, atleast 99.99, at least 99.999, at least 99.9998, or at least 99.9999.

In terms of log reduction (Staphylococcus aureus), the formulation,structure, and/or fibers may demonstrate a log reduction of greater than2.0, e.g., greater than 3.0, greater than 3.5, greater than 4.0, greaterthan 4.5, greater than 4.375, or greater than 5.0.

In terms of log reduction (Klebsiella pneumoniae), the formulation,structure, and/or fibers may demonstrate a log reduction of greater than3.0, e.g., greater than 3.75, greater than 4.0, greater than 4.0,greater than 4.5, greater than 4.75, greater than 5.0, greater than 5.5,or greater than 6.0.

Fiber Dimensions and Distributions

The fibers disclosed herein are microfibers, e.g., fibers having anaverage fiber diameter of less than 25 microns, or nanofibers, e.g.,fibers having an average fiber diameter of less than 1000 nm (1 micron).

In some embodiments, the fibers have an average fiber diameter less thanthe diameter of fibers formed for carpet-related applications, which aregenerally unsuitable for next-to-skin applications, For example thefibers may have an average fiber diameter less than 25 microns, e.g.,less than 20 microns, less than 18 microns, less than 17 microns, lessthan 15 microns, less than 12 microns, less than 10 microns, less than 7microns, less than 5 microns, less than 3 microns, or less than 2microns.

In some cases, the average fiber diameter of the nanofibers in the(fiber layer of the) nonwoven may be less than 1 micron, e.g., less than950 nanometers, less than 925 nanometers, less than 900 nanometers, lessthan 800 nanometers, less than 700 nanometers, less than 600 nanometers,or less than 500 nanometers. In terms of lower limits, the average fiberdiameter of the nanofibers may be at least 100 nanometers, at least 110nanometers, at least 115 nanometers, at least 120 nanometers, at least125 nanometers, at least 130 nanometers, or at least 150 nanometers. Interms of ranges, the average fiber diameter of the nanofibers may befrom 100 to 1000 nanometers, e.g., from 110 to 950 nanometers, from 115to 925 nanometers, from 120 to 900 nanometers, from 125 to 800nanometers, from 125 to 700 nanometers, from 130 to 600 nanometers, orfrom 150 to 500 nanometers. Such average fiber diameters maydifferentiate the nanofibers formed by the spinning methods disclosedherein from nanofibers formed by electrospinning methods.Electrospinning methods typically have average fiber diameters of lessthan 100 nanometers, e.g., from 50 up to less than 100 nanometers.Without being bound by theory, it is believed that such small nanofiberdiameters may result in reduced strength of the fibers and increaseddifficulty in handling the nanofibers. Although some electrospinningmethods may be contemplated.

In some cases, the average fiber diameter of the microfibers in nonwovenmay be less than 25 microns, e.g., less than 24 microns, less than 22microns, less than 20 microns, less than 15 microns, less than 10microns, or less than 5 microns. In terms of lower limits, the averagefiber diameter of the microfibers in the nonwoven may be at least 1micron, at least 2 microns, at least 3 microns, at least 5 microns, atleast 7 microns, or at least 10 microns. In terms of ranges, the averagefiber diameter of the nanofibers in the fiber layer of the nonwoven maybe from 1 to 25 microns, e.g., from 2 to 24 microns, from 3 to 22microns, from 5 to 20 microns, from 7 to 15 microns, from 2 to 10microns, or from 1 to 5 microns. Such average fiber diametersdifferentiate the microfibers formed by the spinning methods disclosedherein from fibers formed by electrospinning methods.

The use of the disclosed methods and formulations leads to a specificand beneficial distribution of fiber diameters. For example, in the caseof nanofibers, less than 20% of the nanofibers may have a fiber diameterfrom greater than 700 nanometers, e.g., less than 17.5%, less than 15%,less than 12.5%, or less than 10%. In terms of lower limits, at least 1%of the nanofibers have a fiber diameter of greater than 700 nanometers,e.g., at least 2%, at least 3%, at least 4%, or at least 5%. In terms ofranges, from 1 to 20% of the nanofibers have a fiber diameter of greaterthan 700 nanometers, e.g., from 2 to 17.5%, from 3 to 15%, from 4 to12.5%, or from 5 to 10%. Such a distribution may differentiate thenanofiber nonwoven products described herein from those formed byelectrospinning (which have a smaller average diameter (50-100nanometers) and a much narrower distribution) and from those formed bynon-nanofiber melt spinning (which have a much greater distribution).For example, a non-nanofiber centrifugally spun nonwoven is disclosed inWO 2017/214085 and reports fiber diameters of 2.08 to 4.4 microns butwith a very broad distribution reported in FIG. 10A of WO 2017/214085.Electrospinning, however, may still be used, depending on the desiredfiber diameter and distribution.

In the case of microfibers, the fiber diameter may also have a desirablynarrow distribution depending on the size of the microfiber. Forexample, less than 20% of the microfibers may have a fiber diametergreater than 2 microns greater than the average fiber diameter, e.g.,less than 17.5%, less than 15%, less than 12.5%, or less than 10%. Interms of lower limits, at least 1% of the microfibers have a fiberdiameter of greater than 2 microns greater than the average fiberdiameter, e.g., at least 2%, at least 3%, at least 4%, or at least 5%.In terms of ranges, from 1 to 20% of the microfibers have a fiberdiameter of greater than 2 microns greater than the average fiberdiameter, e.g., from 2 to 17.5%, from 3 to 15%, from 4 to 12.5%, or from5 to 10%. In further examples, the above recited distributions may bewithin 1.5 microns of the average fiber diameter, e.g., within 1.25microns, within 1 micron, or within 500 nanometers.

In some aspects, combinations of fibers having different average fiberdiameters may be used. For example, a combination of nanofibers andmicrofibers may be used, e.g., a combination of fibers having an averagefiber diameter of less than 1 micron and fibers having an average fiberdiameter from 1 to 25 microns. In further aspects, combinations ofnanofibers having different average fiber diameters may be used. Instill further aspects, combinations of microfibers having differentfiber diameters may be used. In yet further aspects, combinations ofthree, four, five, or more fibers having different fiber diameters maybe used.

In an embodiment, advantages are envisioned having two related polymerswith different RV values (both less than 330 and having an average fiberdiameter less than 1 micron) blended for a desired property. Forexample, the melting point of the polyamide may be increased, the RVadjusted, or other properties adjusted.

In an embodiment, advantages are envisioned having two related polymerswith different RV values (both less than 330 and having an average fiberdiameter as discussed herein) blended for a desired property. Forexample, the melting point of the polyamide may be increased, the RVadjusted, or other properties adjusted.

The antimicrobial fibers and fabrics advantageously have durableantimicrobial properties. In some aspects, the antimicrobial fibers maybe formed from polyamides, polyesters, and blends thereof. Theantimicrobial fibers may be spun to form a nonwoven that imparts theadvantageous antimicrobial properties to textiles, e.g., apparel such asathletic wear or other next-to-skin apparel.

In some embodiments, the polyamide composition is used to produceantimicrobial molded and processed products having permanentantimicrobial properties. In some aspects, a molded and processedproduct comprising the antimicrobial polyamide composition is produced.In some aspects, the polyamide composition can further compriseadditives such as, for example, EBS and polyethylene wax, which are twonon-limiting examples of additives.

In some embodiments, the polyamide composition can be utilized ininjection molding, extrusion molding, blowing, or laminating treatmentmethods after their direct addition during the molding process ofplastics. In other embodiments, the polyamide composition can be addedto form a master batch that is used to form a molded product.

Some embodiments relate to a molded and processed product comprising thepolyamide composition. In some aspects, the molded and processedproducts are industrial supplies, various wrappers, consumer supplies ormedical supplies, and the molded and processed products can be appliedto interior materials such as blinds, wall papers and floor coverings;food related products such as films for wrapping, storage containers,and cutting boards; appliances such as humidifiers, washers, and dishwashers; engineering materials such as water supply and drain pipes, andconcrete; core materials in medical fields; and products for industrialpurposes such as coatings. The molded and processed products areparticularly useful for medical supplies, that is, medicaldevices/products for insertion into the human body such as catheters formedical purposes, prostheses, and products for repairing bones, or bloodtransfusion bags for medical purposes.

RV of Polyamide, Formulation, Structure, and Fibers

RV of polyamides and formulations (and resultant structures andproducts) is generally a ratio of solution or solvent viscositiesmeasured in a capillary viscometer at 25° C. (ASTM D 789) (2015). Forpresent purposes the solvent is formic acid containing 10% by weightwater and 90% by weight formic acid. The solution is 8.4% by weightpolymer dissolved in the solvent.

The RV (η_(r)) as used with respect to the disclosed polymers andproducts is the ratio of the absolute viscosity of the polymer solutionto that of the formic acid:η_(r)=(η_(p)/η_(f))=(f _(r) ×d _(p) ×t _(p))/ηfwhere: d_(p)=density of formic acid-polymer solution at 25° C.,t_(p)=average efflux time for formic acid-polymer solution,η_(f)=absolute viscosity of formic acid, kPa×s(E+6 cP) andf_(r)=viscometer tube factor, mm²/s (cSt)/s=η_(r)/t₃.

A typical calculation for a 50 RV specimen:ηr=(fr×dp×tp)/ηfwhere:

fr=viscometer tube factor, typically 0.485675 cSt/s

dp=density of the polymer—formic solution, typically 1.1900 g/ml

tp=average efflux time for polymer—formic solution, typically 135.00 s

ηf=absolute viscosity of formic acid, typically 1.56 cP

giving an RV of ηr=(0.485675 cSt/s×1.1900 g/ml×135.00 s)/1.56 cP=50.0.The term t₃ is the efflux time of the S-3 calibration oil used in thedetermination of the absolute viscosity of the formic acid as requiredin ASTM D789 (2015).

Advantageously, it has been discovered that adding the above identifiedproportions of zinc and optionally phosphorus may result in a beneficialrelative viscosity of the polyamide formulation, structure, and/orfibers. In some embodiments, the RV ranges from 1 to 100, e.g., from 10to 100, from 20 to 100, from 25 to 80, from 30 to 60, from 40 to 50,from 1 to 40, from 10 to 30, from 15 to 20, from 20 to 35, or from 25 to32. In terms of lower limits, the RV may be greater than 1, e.g.,greater than 10, greater than 15, greater than 20, greater than 25,greater than 30, greater than 35, or greater than 40. In terms of upperlimits, the RV may be less than 100, e.g., less than 80, less than 60,less than 40, less than 35, less than 32, less than 30, or less than 20.

In some embodiments, the RV of the (precursor) polyamide has a lowerlimit of at least 2, e.g., at least 3, at least 4, or at least 5. Interms of upper limits, the polyamide has an RV of at 330 or less, 300 orless, 275 or less, 250 or less, 225 or less, 200 or less, 150 or less,100 or less, or 60 or less. In terms of ranges, the polyamide may havean RV of 2 to 330, e.g., from 2 to 300, from 2 to 275, from 2 to 250,from 2 to 225, from 2 to 200, 2 to 100, from 2 to 60, from 2 to 50, from2 to 40, from 10 to 40, or from 15 to 40 and any values in between.

In some embodiments, the RV of the nonwoven structure has a lower limitof at least 2, e.g., at least 3, at least 4, or at least 5. In terms ofupper limits, the nanofiber nonwoven product has an RV of at 330 orless, 300 or less, 275 or less, 250 or less, 225 or less, 200 or less,150 or less, 100 or less, or 60 or less. In terms of ranges, thenonwoven may have an RV of 2 to 330, e.g., from 2 to 300, from 2 to 275,from 2 to 250, from 2 to 225, from 2 to 200, 2 to 100, from 2 to 60,from 2 to 50, from 2 to 40, from 10 to 40, or from 15 to 40, and anyvalues in between.

The relationship between the RV of the (precursor) polyamide compositionand the RV of the nonwoven structure or the fibers thereof may vary. Insome aspects, the RV of the nonwoven may be lower than the RV of thepolyamide composition. Reducing the RV conventionally has not been adesirable practice when spinning nylon 66. The inventors, however, havediscovered that, in the production of microfibers and nanofibers, it isan advantage. It has been found that the use of lower RV polyamidenylons, e.g., lower RV nylon 66, in a melt spinning method hassurprisingly been found to yield microfiber and nanofiber filamentshaving unexpectedly small filament diameters.

The method by which the RV is lowered may vary widely. In some cases,method temperature may be raised to lower the RV. In some embodiments,however, the temperature raise may only slightly lower the RV sincetemperature affects the kinetics of the reaction, but not the reactionequilibrium constant. The inventors have discovered that, beneficially,the RV of the polyamide, e.g., the nylon 66, may be lowered bydepolymerizing the polymer with the addition of moisture. Up to 5%moisture, e.g., up to 4%, up to 3%, up to 2%, or up to 1%, may beincluded before the polyamide begins to hydrolyze. This techniqueprovides a surprising advantage over the conventional method of addingother polymers, e.g., polypropylene, to the polyamide (to reduce RV).

In some aspects, the RV may be adjusted, e.g., by lowering thetemperature, manipulating the zinc amount, and/or by reducing themoisture. Again, temperature has a relatively modest effect on adjustingthe RV, as compared to moisture content. The moisture content may bereduced to as low as 1 ppm or greater, e.g., 5 ppm or greater, 10 ppm orgreater, 100 ppm or greater, 500 ppm or greater, 1000 ppm or greater, or2500 ppm or greater. Reduction of moisture content is also advantageousfor decreasing TDI and ODI values, discussed further herein. Inclusionof a catalyst may affect the kinetics, but not the actual equilibriumconstant.

In some aspects, the RV of the nonwoven is at least 20% less than the RVof the polyamide prior to spinning, e.g., at least 25% less, at least30% less, at least 35% less, at least 40% less, at least 45% less, or atleast 90% less.

In other aspects, the RV of the nonwoven is at least 5% greater than theRV of the polyamide prior to spinning, e.g., at least 10% greater, atleast 15% greater, at least 20% greater, at least 25% greater, at least30% greater, or at least 35% greater.

In still further aspects, the RV of the polyamide and the RV of thenonwoven may be substantially the same, e.g., within 5% of each other.

An additional embodiment of the present disclosure involves productionof an antimicrobial structure comprising polyamide nanofibers and/ormicrofibers having an average fiber diameter of less than 25 microns,and having an RV of from 2 to 330. In this alternate embodiment,preferable RV ranges include: 2 to 330, e.g., from 2 to 300, from 2 to275, from 2 to 250, from 2 to 225, from 2 to 200, 2 to 100, from 2 to60, from 2 to 50, from 2 to 40, from 10 to 40, or from 15 to 40. Thenanofibers and/or microfibers are subsequently converted to nonwovenweb. As the RV increases beyond about 10 to 30, e.g., 20 to 30,operating temperature becomes a greater parameter to consider. At an RVabove the range of about 10 to 30, e.g., 20 to 30, the temperature mustbe carefully controlled so as the polymer melts for processing purposes.Methods or examples of melt techniques are described in U.S. Pat. No.8,777,599 (incorporated by reference herein), as well as heating andcooling sources which may be used in the apparatuses to independentlycontrol the temperature of the fiber producing device. Non limitingexamples include resistance heaters, radiant heaters, cold gas or heatedgas (air or nitrogen), or conductive, convective, or radiation heattransfer mechanisms.

Nonwoven Polyamide Characteristics

The spinning processes described herein can form an antimicrobialnonwoven polyamide structure (and fibers) having a relatively lowoxidative degradation index (“ODI”) value. A lower ODI indicates lesssevere oxidative degradation during manufacture. In some aspects, theODI may range from 10 to 150 ppm. ODI may be measured using gelpermeation chromatography (GPC) with a fluorescence detector. Theinstrument is calibrated with a quinine external standard. 0.1 grams ofnylon is dissolved in 10 mL of 90% formic acid. The solution is thenanalyzed by GPC with the fluorescence detector. The detector wavelengthsfor ODI are 340 nm for excitation and 415 nm for emission. In terms ofupper limits, the ODI of the antimicrobial nonwoven polyamide may be 200ppm or less, e.g., 180 ppm or less, 150 ppm or less, 125 ppm or less,100 ppm or less, 75 ppm or less, 60 ppm or less, or 50 ppm or less. Interms of the lower limits, the ODI of the antimicrobial nonwovenpolyamide may be 1 ppm or greater, 5 ppm or greater, 10 ppm or greater,15 ppm or greater, 20 ppm or greater, or 25 ppm or greater. In terms ofranges, the ODI of the antimicrobial nonwoven polyamide may be from 1 to200 ppm, from 1 to 180 ppm, from 1 to 150 ppm, from 5 to 125 ppm, from10 to 100 ppm, from 1 to 75 ppm, from 5 to 60 ppm, or from 5 to 50 ppm.

Additionally, the spinning processes as described herein can result in arelatively low thermal degradation index (“TDI”). A lower TDI indicatesa less severe thermal history of the polyamide during manufacture. TDIis measured the same as ODI, except that the detector wavelengths forTDI are 300 nm for excitation and 338 nm for emission. In terms of upperlimits, the TDI of the polyamide nanofiber nonwoven may be 4000 ppm orless, e.g., 3500 ppm or less, 3100 ppm or less, 2500 ppm or less, 2000ppm or less, 1000 ppm or less, 750 ppm or less, or 700 ppm or less. Interms of the lower limits, the TDI of the polyamide nanofiber nonwovenmay be 20 ppm or greater, 100 ppm or greater, 125 ppm or greater, 150ppm or greater, 175 ppm or greater, 200 ppm or greater, or 210 ppm orgreater. In terms of ranges, the TDI of the polyamide nanofiber nonwovenmay be from 20 to 400 ppm, 100 to 4000 ppm, from 125 to 3500 ppm, from150 to 3100 ppm, from 175 to 2500 ppm, from 200 to 2000 ppm, from 210 to1000 ppm, from 200 to 750 ppm, or from 200 to 700 ppm.

TDI and ODI test methods are also disclosed in U.S. Pat. No. 5,411,710.Lower TDI and/or ODI values are beneficial because they indicate thatthe antimicrobial nonwoven polyamide is more durable than productshaving greater TDI and/or ODI. As explained above, TDI and ODI aremeasures of degradation and a product with greater degradation would notperform as well. For example, such a product may have erratic dyeuptake, lower heat stability, lower life in a filtration applicationwhere the fibers are exposed to heat, pressure, oxygen, or anycombination of these, and lower tenacity in industrial fiberapplications.

One possible method that may be used in forming an antimicrobialnonwoven polyamide with a lower TDI and/or ODI would be to includeadditives as described herein, especially antioxidants. Suchantioxidants, although not necessary in conventional processes, may beused to inhibit degradation. An example of useful antioxidants includecopper halides and Nylostab® S-EED® available from Clariant.

The spinning methods as described herein may also result in anantimicrobial nonwoven polyamide structure (or fibers) having an AirPermeability Value of less than 600 CFM/ft², e.g., less than 590CFM/ft², less than 580 CFM/ft², less than 570 CFM/ft², less than 560CFM/ft², or less than 550 CFM/ft². In terms of lower limits, theantimicrobial nonwoven polyamide may have an Air Permeability Value ofat least 50 CFM/ft², at least 75 CFM/ft², at least 100 CFM/ft², at least125 CFM/ft², at least 150 CFM/ft², or at least 200 CFM/ft². In terms ofranges, the antimicrobial nonwoven polyamide may have an AirPermeability Value from 50 to 600 CFM/ft², from 75 to 590 CFM/ft², from100 to 580 CFM/ft², from 125 to 570 CFM/ft², from 150 to 560 CFM/ft², orfrom 200 to 550 CFM/ft².

The spinning methods as described herein may also result in anantimicrobial nonwoven polyamide having a filtration efficiency, asmeasured by a TSI 3160 automated filter tester from 1 to 99.999%, e.g.,from 1 to 95%, from 1 to 90%, from 1.5 to 85%, or from 2 to 80%. The TSI3160 Automated Filter Tester is used to test the efficiency of filtermaterials. Particle penetration and pressure drop are the two importantparameters measured using this instrument. Efficiency is100%-penetration. A challenge solution with known particle size is used.The TSI 3160 is used to measure Hepa filters and uses a DOP solution. Itcombines an Electrostatic Classifier with dual Condensation ParticleCounters (CPCs) to measure most penetrating particle size (MPPS) from 15to 800 nm using monodisperse particles. And can test efficiencies up to99.999999%.

Formulations

In one embodiment, the formulation, structure, and/or fibers compriseless than 3100 ppm of zinc and a delusterant including at least aportion of the phosphorus and may demonstrate a Staphylococcus Aureusreduction of at least 95%, as measured by ISO 20743-13.

In one embodiment, the formulation, structure, and/or fibers comprisefrom 275 ppm to 3100 ppm of zinc and little or no phosphorus andnylon-6,6, as the polyamide, may have an average fiber diameter of lessthan 1 micron; may demonstrate a Staphylococcus Aureus reduction of atleast 95%, and may demonstrate a Klebsiella pneumonia reduction of atleast 99%, as measured by ISO 20743-13.

In one embodiment, the formulation, structure, and/or fibers compriseless than 3100 ppm of zinc and little or no phosphorus and nylon-6,6, asthe polyamide, may have an average fiber diameter of less than 1 micron;may demonstrate a Staphylococcus Aureus reduction of at least 95%, andmay demonstrate a Klebsiella pneumonia reduction of at least 99%, asmeasured by ISO 20743-13.

In one embodiment, the formulation, structure, and/or fibers comprisefrom 200 to 1500 ppm of zinc (optionally provided as zinc oxide and/orzinc stearate) and little or no phosphorus, may have an RV ranging from10 to 30, may have an average fiber diameter of less than 1 micron; maydemonstrate a Staphylococcus Aureus reduction of at least 99%, and maydemonstrate a Klebsiella pneumonia reduction of at least 99.9%, asmeasured by ISO 20743-13.

In another embodiment, the polymer comprises a nylon-based polymer, thezinc is provided via zinc oxide and/or zinc pyrithione, and the relativeviscosity of the polyamide composition ranges from 10 to 100, e.g., 20to 100.

In yet another embodiment, the polymer comprises nylon-6,6, the zinc isprovided via zinc oxide, the weight ratio of zinc to phosphorus is atleast 2:1, and the polyamide composition may demonstrate aStaphylococcus Aureus reduction of at least 95%, as measured by ISO20743-13.

In one embodiment, the antimicrobial fibers comprise the polymercomprising less than 500 ppm of zinc, a delusterant including at least aportion of the phosphorus, and the antimicrobial fibers demonstrate aStaphylococcus Aureus reduction of at least 90%.

In another embodiment, the antimicrobial fibers comprise the polymercomprising nylon, the zinc is provided in the form of zinc oxide and/orzinc pyrithione, the relative viscosity of the polyamide compositionranges from 10 to 100, e.g., 20 to 100, and the fibers have a zincretention greater than 80% as measured by a dye bath test, and thefibers have an average diameter less than 18 microns.

In yet another embodiment, the antimicrobial fibers comprise the polymercomprising nylon-6,6, the zinc is provided in the form of zinc oxide,the weight ratio of zinc to phosphorus is at least 2:1, the fibers maydemonstrate a Staphylococcus Aureus reduction of at least 95%, asmeasured by ISO 20743-13, the fibers have a zinc retention greater than90% as measured by a dye bath test, and the antimicrobial fibers have anaverage diameter less than 10 microns.

Method of Forming Fibers, Nonwoven Structure

As described herein, the antimicrobial nonwoven polyamide structure isformed by spinning the formulation to form the fibers, which arearranged to form the structure.

In some embodiments, the present disclosure provides a process forimparting permanent antimicrobial properties to nonwoven fibers andstructures and fabrics made from the polyamide formulations describedherein. In some aspects, the fibers, e.g., polyamide fibers, are made byspinning a polyamide formed in a melt polymerization process. During themelt polymerization process of the polyamide composition, an aqueousmonomer solution, e.g., salt solution, is heated under controlledconditions of temperature, time and pressure to evaporate water andeffect polymerization of the monomers, resulting in a polymer melt.During the melt polymerization process, sufficient amounts of zinc and,optionally, phosphorus, are employed in the aqueous monomer solution toform the polyamide mixture before polymerization. The monomers areselected based on the desired polyamide composition. After zinc andphosphorus are present in the aqueous monomer solution, the polyamidecomposition may be polymerized. The polymerized polyamide cansubsequently be spun into fibers, e.g., by melt, solution, centrifugal,or electro-spinning.

In some embodiments, the process for preparing antimicrobial fibershaving permanent antimicrobial properties from the polyamide compositionincludes preparing an aqueous monomer solution, adding less than 2000ppm zinc dispersed within the aqueous monomer solution, e.g., less than1500 ppm, less than 1000 ppm, less than 750 ppm, less than 500 ppm, orless than 400 ppm, and adding less than 2000 ppm phosphorus, e.g., lessthan 1500 ppm, less than 1000 ppm, less than 750 ppm, less than 500 ppm,or less than 400 ppm, polymerizing the aqueous monomer solution to forma polymer melt, and spinning the polymer melt to form an antimicrobialfiber. In this embodiment, the polyamide composition comprises theresultant aqueous monomer solution after zinc and phosphorus are added.

In some embodiments, the process includes preparing an aqueous monomersolution. The aqueous monomer solution may comprise amide monomers. Insome embodiments, the concentration of monomers in the aqueous monomersolution is less than 60 wt %, e.g., less than 58 wt %, less than 56.5wt %, less than 55 wt %, less than 50 wt %, less than 45 wt %, less than40 wt %, less than 35 wt %, or less than 30 wt %. In some embodiments,the concentration of monomers in the aqueous monomer solution is greaterthan 20 wt %, e.g., greater than 25 wt %, greater than 30 wt %, greaterthan 35 wt %, greater than 40 wt %, greater than 45 wt %, greater than50 wt %, greater than 55 wt %, or greater than 58 wt %. In someembodiments, the concentration of monomers in the aqueous monomersolution is in a range from 20 wt % to 60 wt %, e.g., from 25 wt % to 58wt %, from 30 wt % to 56.5 wt %, from 35 wt % to 55 wt %, from 40 wt %to 50 wt %, or from 45 wt % to 55 wt %. The balance of the aqueousmonomer solution may comprise water and/or additional additives. In someembodiments, the monomers comprise amide monomers including a diacid anda diamine, i.e., nylon salt.

In some embodiments, the aqueous monomer solution is a nylon saltsolution. The nylon salt solution may be formed by mixing a diamine anda diacid with water. For example, water, diamine, and dicarboxylic acidmonomer are mixed to form a salt solution, e.g., mixing adipic acid andhexamethylene diamine with water. In some embodiments, the diacid may bea dicarboxylic acid and may be selected from the group consisting ofoxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid,adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioicacid, dodecandioic acid, maleic acid, glutaconic acid, traumatic acid,and muconic acid, 1,2- or 1,3-cyclohexane dicarboxylic acids, 1,2- or1,3-phenyl enediacetic acids, 1,2- or 1,3-cyclohexane diacetic acids,isophthalic acid, terephthalic acid, 4,4′-oxybisbenzoic acid,4,4-benzophenone dicarboxylic acid, 2,6-napthalene dicarboxylic acid,p-t-butyl isophthalic acid and 2,5-furandicarboxylic acid, and mixturesthereof. In some embodiments, the diamine may be selected from the groupconsisting of ethanol diamine, trimethylene diamine, putrescine,cadaverine, hexamethyelene diamine, 2-methyl pentamethylene diamine,heptamethylene diamine, 2-methyl hexamethylene diamine, 3-methylhexamethylene diamine, 2,2-dimethyl pentamethylene diamine,octamethylene diamine, 2,5-dimethyl hexamethylene diamine, nonamethylenediamine, 2,2,4- and 2,4,4-trimethyl hexamethylene diamines,decamethylene diamine, 5-methylnonane diamine, isophorone diamine,undecamethylene diamine, dodecamethylene diamine, 2,2,7,7-tetramethyloctamethylene diamine, bis(p-aminocyclohexyl)methane,bis(aminomethyl)norbornane, C2-C16 aliphatic diamine optionallysubstituted with one or more C1 to C4 alkyl groups, aliphatic polyetherdiamines and furanic diamines, such as 2,5-bis(aminomethyl)furan, andmixtures thereof. In preferred embodiments, the diacid is adipic acidand the diamine is hexamethylene diamine which are polymerized to formnylon 6,6.

It should be understood that the concept of producing a polyamide fromdiamines and diacids also encompasses the concept of other suitablemonomers, such as, aminoacids or lactams. Without limiting the scope,examples of aminoacids can include 6-aminohaxanoic acid,7-aminoheptanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid,or combinations thereof. Without limiting the scope of the disclosure,examples of lactams can include caprolactam, enantholactam,lauryllactam, or combinations thereof. Suitable feeds for the disclosedprocess can include mixtures of diamines, diacids, aminoacids andlactams.

After the aqueous monomer solution is prepared, zinc is added to theaqueous monomer solution to form the polyamide composition. In someembodiments, less than 2000 ppm of zinc is dispersed within the aqueousmonomer solution. In some aspects, further additives, e.g., additionalantimicrobial agents, are added to the aqueous monomer solution.Optionally, phosphorus is added to the aqueous monomer solution.

In some cases, the polyamide composition is polymerized using aconventional melt polymerization process. In one aspect, the aqueousmonomer solution is heated under controlled conditions of time,temperature, and pressure to evaporate water, effect polymerization ofthe monomers and provide a polymer melt. In some aspects, the particularweight ratio of zinc to phosphorus may advantageously promote binding ofzinc within the polymer, reduce thermal degradation of the polymer, andenhance its dyeability.

In some aspects, an antimicrobial nylon is prepared by a conventionalmelt polymerization of a nylon salt. Typically, the nylon salt solutionis heated under pressure (e.g. 250 psig/1825×10³ n/m²) to a temperatureof, for example, about 245° C. Then the water vapor is exhausted off byreducing the pressure to atmospheric pressure while increasing thetemperature to, for example, about 270° C. Before polymerization, zincand, optionally, phosphorus be added to the nylon salt solution. Theresulting molten nylon is held at this temperature for a period of timeto bring it to equilibrium prior to being extruded into a fiber. In someaspects, the process may be carried out in a batch or continuousprocess.

In some embodiments, during melt polymerization, zinc, e.g., zinc oxideis added to the aqueous monomer solution. The antimicrobial fiber maycomprise a polyamide that is made in a melt polymerization process andnot in a master batch process. In some aspects, the resulting fiber haspermanent antimicrobial properties. The resulting fiber can be used forapplications such as, e.g., socks, heavy hosiery, and shoes.

The antimicrobial agent may be added to the polyamide during meltpolymerization, for example as a master batch or as a powder added tothe polyamide pellets, and thereafter, the fiber may be formed fromspinning. The fibers are then formed into a nonwoven

In some aspects, the antimicrobial nonwoven structure is melt blown.Melt blowing is advantageously less expensive than electrospinning. Meltblowing is a process type developed for the formation of microfibers andnonwoven webs. Until recently, microfibers have been produced by meltblowing. Now, nanofibers may also be formed by melt blowing. Thenanofibers are formed by extruding a molten thermoplastic polymericmaterial, or polyamide, through a plurality of small holes. Theresulting molten threads or filaments pass into converging high velocitygas streams which attenuate or draw the filaments of molten polyamide toreduce their diameters. Thereafter, the melt blown nanofibers arecarried by the high velocity gas stream and deposited on a collectingsurface, or forming wire, to form a nonwoven web of randomly disbursedmelt blown nanofibers. The formation of nanofibers and nonwoven webs bymelt blowing is well known in the art. See, by way of example, U.S. Pat.Nos. 3,704,198; 3,755,527; 3,849,241; 3,978,185; 4,100,324; and4,663,220.

One option, “Island-in-the-sea,” refers to fibers forming by extrudingat least two polymer components from one spinning die, also referred toas conjugate spinning.

As is well known, electrospinning has many fabrication parameters thatmay limit spinning certain materials. These parameters include:electrical charge of the spinning material and the spinning materialsolution; solution delivery (often a stream of material ejected from asyringe); charge at the jet; electrical discharge of the fibrousmembrane at the collector; external forces from the electrical field onthe spinning jet; density of expelled jet; and (high) voltage of theelectrodes and geometry of the collector. In contrast, theaforementioned nanofibers and products are advantageously formed withoutthe use of an applied electrical field as the primary expulsion force,as is required in an electrospinning process. Thus, the polyamide is notelectrically charged, nor are any components of the spinning process.Importantly, the dangerous high voltage necessary in electrospinningprocesses, is not required with the presently disclosedprocesses/products. In some embodiments, the process is anon-electrospin process and resultant product is a non-electrospunproduct that is produced via a non-electrospin process.

An embodiment of making the inventive nanofiber nonwovens is by way of2-phase spinning or melt blowing with propellant gas through a spinningchannel as is described generally in U.S. Pat. No. 8,668,854. Thisprocess includes two phase flow of polymer or polymer solution and apressurized propellant gas (typically air) to a thin, preferablyconverging channel. The channel is usually and preferably annular inconfiguration. It is believed that the polymer is sheared by gas flowwithin the thin, preferably converging channel, creating polymeric filmlayers on both sides of the channel. These polymeric film layers arefurther sheared into nanofibers by the propellant gas flow. Here again,a moving collector belt may be used and the basis weight of thenanofiber nonwoven is controlled by regulating the speed of the belt.The distance of the collector may also be used to control fineness ofthe nanofiber nonwoven. The process is better understood with referenceto FIG. 1 .

Beneficially, the use of the aforementioned polyamide precursor in themelt spinning process provides for significant benefits in productionrate, e.g., at least 5% greater, at least 10% greater, at least 20%greater, at least 30% greater, at least 40% greater. The improvementsmay be observed as an improvement in area per hour versus a conventionalprocess, e.g., another process that does not employ the featuresdescribed herein. In some cases, the production increase over aconsistent period of time is improved. For example, over a given timeperiod, e.g., one hour, of production, the disclosed process produces atleast 5% more product than a conventional process or an electrospinprocess, e.g., at least 10% more, at least 20% more, at least 30% more,or at least 40% more.

FIG. 1 illustrates schematically operation of a system for spinning ananofiber nonwoven including a polyamide feed assembly 110, an air feed1210 a spinning cylinder 130, a collector belt 140 and a take up reel150. During operation, polyamide melt or solution is fed to spinningcylinder 130 where it flows through a thin channel in the cylinder withhigh pressure air, shearing the polyamide into nanofibers. Details areprovided in the aforementioned U.S. Pat. No. 8,668,854. The throughputrate and basis weight is controlled by the speed of a gear pump and thespeed of the belt. Optionally, functional additives such as charcoals,copper or the like can be added with the air feed, if so desired.

In an alternate construction of the spinneret used in the system of FIG.1 , particulate material may be added with a separate inlet as is seenin U.S. Pat. No. 8,808,594.

Still yet another methodology which may be employed is melt blowing thepolyamide nanofiber webs disclosed herein (FIG. 2 ). Melt blowinginvolves extruding the polyamide into a relatively high velocity,typically hot, gas stream. To produce suitable nanofibers, carefulselection of the orifice and capillary geometry as well as thetemperature is required as is seen in: Hassan et al., J Membrane Sci.,427, 336-344, 2013 and Ellison et al., Polymer, 48 (11), 3306-3316,2007, and, International Nonwoven Journal, Summer 2003, pg 21-28.

U.S. Pat. No. 7,300,272 discloses a fiber extrusion pack for extrudingmolten material to form an array of nanofibers that includes a number ofsplit distribution plates arranged in a stack such that each splitdistribution plate forms a layer within the fiber extrusion pack, andfeatures on the split distribution plates form a distribution networkthat delivers the molten material to orifices in the fiber extrusionpack. Each of the split distribution plates includes a set of platesegments with a gap disposed between adjacent plate segments. Adjacentedges of the plate segments are shaped to form reservoirs along the gap,and sealing plugs are disposed in the reservoirs to prevent the moltenmaterial from leaking from the gaps. The sealing plugs can be formed bythe molten material that leaks into the gap and collects and solidifiesin the reservoirs or by placing a plugging material in the reservoirs atpack assembly. This pack can be used to make nanofibers with a meltblowing system described in the patents previously mentioned.

In one embodiment, a process for preparing the antimicrobial nonwovenpolyamide structure is disclosed. The process comprising the step offorming a (precursor) polyamide (preparation of monomer solutions arewell known), e.g., by preparing an aqueous monomer solution. Duringpreparation of the precursor zinc is added (as discussed herein). Insome cases, the zinc is added to (and dispersed in) the aqueous monomersolution.

Phosphorus may also be added. In some cases, the precursor ispolymerized to form a polyamide composition. The process furthercomprises the steps of spinning the polyamide to form antimicrobialpolyamide fibers and forming the antimicrobial polyamide fibers intoantimicrobial nonwoven structure. In some cases, the polyamidecomposition is melt spun, spunbonded, electrospun, solution spun, orcentrifugally spun.

Beneficially, the spinning may take place at low die pressures, whichhave been found to decrease or eliminate detrimental fiber formationinterruptions, which create defects in the web structure. In someembodiments, the spinning may be conducted at a die pressure less than300 psig, e.g., less than 275 psig, less than 272 psig, less than 250psig, less than 240 psig, less than 200 psig, less than 190 psig, lessthan 175 psig, less than 160 psig, or less than 155 psig. In terms ofranges, the spinning may be conducted at a die pressure ranging from 10psig to 300 psig, e.g., from 25 psig to 275 psig, from 35 psig to 272psig, from 50 psig to 250 psig, from 75 psig to 240 psig, from 75 psigto 200 psig, or from 90 psig to 155 psig.

In some embodiments, there is disclosed a process for preparingantimicrobial nonwoven fibers, optionally in a structure as discussedabove. The process comprises the step of preparing a formulationcomprising a polyamide, zinc dispersed within the polyamide; and lessthan 2000 ppm phosphorus dispersed within the polyamide. The processcomprises the step of spinning the formulation to form antimicrobialpolyamide fibers, which have the composition and characteristicsdescribed herein. The process further comprises the step of forming theantimicrobial polyamide fibers into antimicrobial nonwoven polyamidestructure. The spinning is conducted at the low die pressures discussedabove.

A fabric can be made from the nonwoven fibers. Garments made from thesefabrics can withstand normal wear, and are devoid of any coated, doped,or topical treatment, which tend to abrade off during knitting andweaving. The abrasion process results in dust on machines and fabric,and lowers the effective use time of garments in normal wear andlaundering.

Polyamide

As described herein, an antimicrobial polyamide composition is used asthe polymer for the nonwoven. As used herein, “polyamide composition”and like terminology refers to compositions containing polyamidesincluding copolymers, terpolymers, polymer blends, alloys andderivatives of polyamides. Further, as used herein, a “polyamide” refersto a polymer, having as a component, a polymer with the linkage of anamino group of one molecule and a carboxylic acid group of anothermolecule. In some aspects, the polyamide is the component present in thegreatest amount. For example, a polyamide containing 40 wt. % nylon 6,30 wt. % polyethylene, and 30 wt. % polypropylene is referred to hereinas a polyamide since the nylon 6 component is present in the greatestamount. Additionally, a polyamide containing 20 wt. % nylon 6, 20 wt. %nylon 66, 30 wt. % polyethylene, and 30 wt. % polypropylene is alsoreferred to herein as a polyamide since the nylon 6 and nylon 66components, in total are the components present in the greatest amount.

Exemplary polyamides and polyamide compositions are described inKirk-Othmer, Encyclopedia of Chemical Technology, Vol. 18, pp. 328-371(Wiley 1982), the disclosure of which is incorporated by reference.

Briefly, polyamides are generally known as compounds that containrecurring amide groups as integral parts of the main polymer chains.Linear polyamides are of particular interest and may be formed fromcondensation of bifunctional monomers. Polyamides are frequentlyreferred to as nylons. Although they generally are considered ascondensation polymers, polyamides may also be formed by ring openingpolymerization. This method of preparation is especially important forsome polymers in which the monomers are cyclic lactams, e.g., Nylon 6.Particular polymers and copolymers and their preparation are seen in thefollowing patents: U.S. Pat. Nos. 4,760,129; 5,504,185; 5,543,495;5,698,658; 6,011,134; 6,136,947; 6,169,162; 7,138,482; 7,381,788; and8,759,475.

There are numerous advantages of using polyamides in commercialapplications. Nylons are generally chemical and temperature resistant,resulting in superior performance to other polymers. They are also knownto have improved strength, elongation, and abrasion resistance ascompared to other polymers. Nylons are also very versatile, allowing fortheir use in a variety of applications.

A class of polyamides particularly preferred for some applicationsincludes High Temperature Nylons (HTN's) as are described in Glasscocket al., High Performance Polyamides Fulfill Demanding Requirements forAutomotive Thermal Management Components, (DuPont),http://www2.dupont.com/Automotive/en_US/assets/downloads/knowledge%20center/HTN-whitepaper-R8.pdfavailable online Jun. 10, 2016. Such polyamides typically include one ormore of the structures seen in the following:

Non-limiting examples of polymers included in the polyamides includepolyamides with combinations of other polymers such as polypropylene andcopolymers, polyethylene and copolymers, polyesters, polystyrenes,polyurethanes, and combinations thereof. Thermoplastic polymers andbiodegradable polymers are also suitable for melt blowing or meltspinning into nanofibers of the present disclosure. As discussed herein,the polymers may be melt spun or melt blown, with a preference for meltspinning or melt blowing by 2-phase propellant-gas spinning, includingextruding the polyamide composition in liquid form with pressurized gasthrough a fiber-forming channel. Other processes to form nonwovenstructures may also be used, including spunbonding, solution spinning,and centrifugal spinning.

Melt points of nylon nanofiber products described herein, includingcopolymers and terpolymers, may be between 223° C. and 390° C., e.g.,from 223 to 380, or from 225° C. to 350° C. Additionally, the melt pointmay be greater than that of conventional nylon 66 melt points dependingon any additional polymer materials that are added.

Other polymer materials that can be used in the antimicrobial nanofibernonwovens of the disclosure include both addition polymer andcondensation polymer materials such as polyolefin, polyacetal, polyamide(as previously discussed), polyester, cellulose ether and ester,polyalkylene sulfide, polyarylene oxide, polysulfone, modifiedpolysulfone polymers and mixtures thereof. Preferred materials that fallwithin these generic classes include polyamides, polyethylene,polyethylene terephthalate (PET), polybutylene terephthalate (PBT),polytrimethylene terephthalate (PTT), polypropylene,poly(vinylchloride), polymethylmethacrylate (and other acrylic resins),polystyrene, and copolymers thereof (including ABA type blockcopolymers), poly(vinylidene fluoride), poly(vinylidene chloride),polyvinylalcohol in various degrees of hydrolysis (87% to 99.5%) incrosslinked and non-crosslinked forms. Addition polymers tend to beglassy (a Tg greater than room temperature). This is the case forpolyvinylchloride and polymethylmethacrylate, polystyrene polymercompositions or alloys or low in crystallinity for polyvinylidenefluoride and polyvinylalcohol materials. Nylon copolymers embodiedherein, can be made by combining various diamine compounds, variousdiacid compounds and various cyclic lactam structures in a reactionmixture and then forming the nylon with randomly positioned monomericmaterials in a polyamide structure. For example, a nylon 66-6,10material is a nylon manufactured from hexamethylene diamine and a C6 anda C10 blend of diacids. A nylon 6-66-6,10 is a nylon manufactured bycopolymerization of epsilonaminocaproic acid, hexamethylene diamine anda blend of a C6 and a C10 diacid material.

In some embodiments, such as that described in U.S. Pat. No. 5,913,993,a small amount of polyethylene polymer can be blended with a nyloncompound used to form a nanofiber nonwoven fabric with desirablecharacteristics. The addition of polyethylene to nylon enhances specificproperties such as softness. The use of polyethylene also lowers cost ofproduction, and eases further downstream processing such as bonding toother fabrics or itself. The improved fabric can be made by adding asmall amount of polyethylene to the nylon feed material used inproducing a nanofiber melt blown fabric. More specifically, the fabriccan be produced by forming a blend of polyethylene and nylon 66,extruding the blend in the form of a plurality of continuous filaments,directing the filaments through a die to melt blow the filaments,depositing the filaments onto a collection surface such that a web isformed.

The polyethylene useful in the process of this embodiment of the subjectdisclosure preferably may have a melt index between about 5 grams/10 minand about 200 grams/10 min and, e.g., between about 17 grams/10 min andabout 150 grams/10 min. The polyethylene should preferably have adensity between about 0.85 grams/cc and about 1.1 grams/cc and, e.g.,between about 0.93 grams/cc and about 0.95 grams/cc. Most preferably,the melt index of the polyethylene is about 150 and the density is about0.93.

The polyethylene used in the process of this embodiment of the subjectdisclosure can be added at a concentration of about 0.05% to about 20%.In a preferred embodiment, the concentration of polyethylene will bebetween about 0.1% and about 1.2%. Most preferably, the polyethylenewill be present at about 0.5%. The concentration of polyethylene in thefabric produced according to the method described will be approximatelyequal to the percentage of polyethylene added during the manufacturingprocess. Thus, the percentage of polyethylene in the fabrics of thisembodiment of the subject disclosure will typically range from about0.05% to about 20% and will preferably be about 0.5%. Therefore, thefabric will typically comprise between about 80 and about 99.95 percentby weight of nylon. The filament extrusion step can be carried outbetween about 250° C. and about 325° C. Preferably, the temperaturerange is about 280° C. to about 315° C. but may be lower if nylon 6 isused.

The blend or copolymer of polyethylene and nylon can be formed in anysuitable manner. Typically, the nylon compound will be nylon 66;however, other polyamides of the nylon family can be used. Also,mixtures of nylons can be used. In one specific example, polyethylene isblended with a mixture of nylon 6 and nylon 66. The polyethylene andnylon polymers are typically supplied in the form of pellets, chips,flakes, and the like. The desired amount of the polyethylene pellets orchips can be blended with the nylon pellets or chips in a suitablemixing device such as a rotary drum tumbler or the like, and theresulting blend can be introduced into the feed hopper of theconventional extruder or the melt blowing line. The blend or copolymercan also be produced by introducing the appropriate mixture into acontinuous polymerization spinning system.

Further, differing species of a general polymeric genus can be blended.For example, a high molecular weight styrene material can be blendedwith a low molecular weight, high impact polystyrene. A Nylon-6 materialcan be blended with a nylon copolymer such as a Nylon-6; 66; 6,10copolymer. Further, a polyvinylalcohol having a low degree of hydrolysissuch as a 87% hydrolyzed polyvinylalcohol can be blended with a fully orsuperhydrolyzed polyvinylalcohol having a degree of hydrolysis between98 and 99.9% and higher. All of these materials in admixture can becrosslinked using appropriate crosslinking mechanisms. Nylons can becrosslinked using crosslinking agents that are reactive with thenitrogen atom in the amide linkage. Polyvinyl alcohol materials can becrosslinked using hydroxyl reactive materials such as monoaldehydes,such as formaldehyde, ureas, melamine-formaldehyde resin and itsanalogues, boric acids and other inorganic compounds, dialdehydes,diacids, urethanes, epoxies and other known crosslinking agents.Crosslinking technology is a well-known and understood phenomenon inwhich a crosslinking reagent reacts and forms covalent bonds betweenpolymer chains to substantially improve molecular weight, chemicalresistance, overall strength and resistance to mechanical degradation.

One preferred mode is a polyamide comprising a first polymer and asecond, but different polymer (differing in polymer type, molecularweight or physical property) that is conditioned or treated at elevatedtemperature. The polymer blend can be reacted and formed into a singlechemical specie. Preferred materials are chemically reacted into asingle polymeric specie such that a Differential Scanning calorimeter(DSC) analysis reveals a single polymeric material to yield improvedstability when contacted with high temperature, high humidity anddifficult operating conditions. Preferred materials for use in theblended polymeric systems include nylon 6; nylon 66; nylon 6,10; nylon(6-66-6,10) copolymers and other linear generally aliphatic nyloncompositions.

A suitable polyamide may include for example, 20% nylon 6, 60% nylon 66and 20% by weight of a polyester. The polyamide may include combinationsof miscible polymers or combinations of immiscible polymers.

In some aspects, the polyamide may include nylon 6. In terms of lowerlimits, the polyamide may include nylon 6 in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 6 in an amount of 99.9 wt. % or less, 99 wt.% or less, 95 wt. % or less, 90 wt. % or less, 85 wt. % or less, or 80wt. % or less. In terms of ranges, the polyamide may comprise nylon 6 inan amount from 0.1 to 99.9 wt. %, e.g., from 1 to 99 wt. %, from 5 to 95wt. %, from 10 to 90 wt. %, from 15 to 85 wt. %, or from 20 to 80 wt. %.

In some aspects, the polyamide may include nylon 66. In terms of lowerlimits, the polyamide may include nylon 66 in an amount of at least 0.1wt. %, e.g., at least 1 wt. %, at least 5 wt. %, at least 10 wt. %, atleast 15 wt. %, or at least 20 wt. %. In terms of upper limits, thepolyamide may include nylon 66 in an amount of 99.9 wt. % or less, 99wt. % or less, 95 wt. % or less, 90 wt. % or less, 85 wt. % or less, or80 wt. % or less. In terms of ranges, the polyamide may comprise nylon66 in an amount from 0.1 to 99.9 wt. %, e.g., from 1 to 99 wt. %, from 5to 95 wt. %, from 10 to 90 wt. %, from 15 to 85 wt. %, or from 20 to 80wt. %.

In some aspects, the polyamide may include nylon 6I, wherein I meansisophthalic acid. In terms of lower limits, the polyamide may includenylon 6I in an amount of at least 0.1 wt. %, e.g., at least 0.5 wt. %,at least 1 wt. %, at least 5 wt. %, at least 7.5 wt. %, or at least 10wt. %. In terms of upper limits, the polyamide may include nylon 6I inan amount of 50 wt. % or less, 40 wt. % or less, 35 wt. % or less, 30wt. % or less, 25 wt. % or less, or 20 wt. % or less. In terms ofranges, the polyamide may comprise nylon 6I in an amount from 0.1 to 50wt. %, e.g., from 0.5 to 40 wt. %, from 1 to 35 wt. %, from 5 to 30 wt.%, from 7.5 to 25 wt. %, or from 10 to 20 wt. %.

In some aspects, the polyamide may include nylon 6T, wherein T meansterephthalic acid. In terms of lower limits, the polyamide may includenylon 6T in an amount of at least 0.1 wt. %, e.g., at least 1 wt. %, atleast 5 wt. %, at least 10 wt. %, at least 15 wt. %, or at least 20 wt.%. In terms of upper limits, the polyamide may include nylon 6T in anamount of 50 wt. % or less, 47.5 wt. % or less, 45 wt. % or less, 42.5wt. % or less, 40 wt. % or less, or 37.5 wt. % or less. In terms ofranges, the polyamide may comprise nylon 6T in an amount from 0.1 to 50wt. %, e.g., from 1 to 47.5 wt. %, from 5 to 45 wt. %, from 10 to 42.5wt. %, from 15 to 40 wt. %, or from 20 to 37.5 wt. %.

Block copolymers are also useful in the process of this disclosure. Withsuch copolymers the choice of solvent swelling agent is important. Theselected solvent is such that both blocks were soluble in the solvent.One example is an ABA (styrene-EP-styrene) or AB (styrene-EP) polymer inmethylene chloride solvent. If one component is not soluble in thesolvent, it will form a gel. Examples of such block copolymers areKraton® type of styrene-b-butadiene and styrene-b-hydrogenated butadiene(ethylene propylene), Pebax® type of e-caprolactam-b-ethylene oxide,Sympatex® polyester-b-ethylene oxide and polyurethanes of ethylene oxideand isocyanates.

Addition polymers like polyvinylidene fluoride, syndiotacticpolystyrene, copolymer of vinylidene fluoride and hexafluoropropylene,polyvinyl alcohol, polyvinyl acetate, amorphous addition polymers, suchas poly(acrylonitrile) and its copolymers with acrylic acid andmethacrylates, polystyrene, poly(vinyl chloride) and its variouscopolymers, poly(methyl methacrylate) and its various copolymers, areknown to be solution spun with relative ease because they are soluble atlow pressures and temperatures. It is envisioned these can be melt spunper the instant disclosure as one method of making nanofibers.

There is a substantial advantage to forming polymeric compositionscomprising two or more polymeric materials in polymer admixture, alloyformat or in a crosslinked chemically bonded structure. We believe suchpolymer compositions improve physical properties by changing polymerattributes such as improving polymer chain flexibility or chainmobility, increasing overall molecular weight and providingreinforcement through the formation of networks of polymeric materials.

In one embodiment of this concept, two related polymer materials can beblended for beneficial properties. For example, a high molecular weightpolyvinylchloride can be blended with a low molecular weightpolyvinylchloride. Similarly, a high molecular weight nylon material canbe blended with a low molecular weight nylon material.

It has surprisingly been found that these polyamides, when utilized withthe aforementioned zinc and/or phosphorus additives and formed intofabrics, may provide odor control features. In some cases, it has beenfound that conventional polymer resins that utilize polyester polymerresins harbor and allow to flourish different types of bacteria, ascompared to those of nylon. For example, micrococcus bacteria have beenfound to flourish in polyester-based fabrics. Thus, the use ofpolyamide-based polymers, specifically nylon-based polymers, along withthe aforementioned additives, surprisingly has been found to yieldfabrics that demonstrate significantly low odor levels as compared tosimilar fabrics that utilize polyesters.

EXAMPLES Examples 1-6 and Comparative Examples A-E

Precursor polyamide compositions were prepared using the componentslisted in Table 1a. For zinc oxide samples, a masterbatch of zinc oxidein nylon 6 was blended with nylon 6,6 flake to achieve the desired zincamount. For zinc stearate samples, the zinc stearate was added as apowder onto the nylon 6,6 flake and processed through a twin screwextruder to achieve the desired zinc amount and to distribute thematerial through the polymer. For copper acetate samples, copper acetatewas added to the salt solution so as to achieve the copper amount.

TABLE 1a Precursor Compositions Sample Zn compound Zn amount, ppm RV A —0 n/a B — 11 24.2 C — Trace* 30.2 D — 0 n/a E Cu acetate 60 n/a 1 ZnOxide 291 19.4 2 Zn Oxide 483 18.3 3 Zn Oxide 692 17.3 4 Zn Oxide 135415.6 5 Zn Stearate 512 18.3 6 Zn Stearate 522 16.3 *a trace amount ofzinc (32) was present due to residual trace amounts in the equipment

Utilizing a conventional melt blowing system, the precursor compositionswere blown into fibers. The fibers were positioned on a scrim that waspositioned on moving belt. Nonwoven webs thus formed. The processemployed an extruder with a high compression screw. The (precursor)polyamide die temperature was approximately 323° C. and air was used asthe gas.

As noted above, the fibers were spun onto a scrim, which was employed toadd integrity to the inventive (nano) fiber web. The polyamides had theRVs listed in Table 1 (before spinning).

The webs were tested for antimicrobial efficacy (according toISO20743-13:2013). The results are shown in Table 1b.

TABLE 1b Test Results Staphylococcus aureus Klebsiella pneumoniae Logreduction % Reduction Log reduction % Reduction (after 24 (after 24(after 24 (after 24 hours) hours) hours) hours) A — — — — B 0.67 78.6%0.23 40.8% C 0.60 74.8% 1.92 98.8% D 0.37 57.5% 0.11 21.5% E 1.26 94.50.16 31.0% 1 5.08 99.999% 4.88 99.999%  2 4.55 99.997% 5.81 99.9998%   35.42 99.9996% 5.64 99.9998%   4 3.68 99.98% 8.20 99.999999%    5 4.9499.999% 6.52 99.99997%   6 4.90 99.999% 6.54 99.99997%  

As shown in Table 1a, the webs that comprised the disclosed amounts ofzinc, demonstrated a surprisingly high reduction (after 24 hours) ofboth Staphylococcus aureus and Klebsiella pneumoniae, e.g., reductiongreater than 99.97% in all cases. In contrast, Comparative examples A-E,which employed little or no zinc compound (or elemental zinc)demonstrated reduction less than 95% for Staphylococcus aureus and lessthan 98.9% for Klebsiella pneumoniae—in most cases, well below 80%.

In particular, the webs demonstrated particularly good reduction ofKlebsiella pneumoniae, e.g., at least 99.999%, versus ComparativeExamples A-D (only 98.8% for Comparative Example C and well below 50%for Comparative Examples A, B, and D. Importantly, the disclosed websdemonstrated superior performance over other metals, e.g., copper inComparative Example E, (99.999+ for Examples 1-6 versus only 31.0% forComparative Example E).

The log reduction numbers are often used in the industry as a measure ofefficacy because these numbers emphasize the differentiation at theupper end of the reduction percentages, e.g., the reduction percentagesover 99.9%.

In terms of microbe growth, log reductions convey how effective aproduct is. The greater the log reduction the more effective the productis at controlling microbe growth. In some cases, during product efficacytesting, the number of colony forming units (CFUs) are counted at thestart of the test. Reduction is then measured over a predetermined time,e.g., 24 hours. The result of the difference between the control and thetest product is then expressed as the log reduction.

As shown in Table 1b, for Klebsiella pneumoniae, the disclosed websdemonstrated a log reduction of well over 2, e.g., greater than 4.5 inmost cases. In contrast, Comparative Examples A-E, including ComparativeExample E, which employed a copper compound as the antimicrobial agent,demonstrated log reductions less than 2, e.g., less than 1.0 in mostcases.

The performance of Staphylococcus aureus was also unexpectedly good. Thewebs demonstrated reduction of Staphylococcus aureus of at least 99.98%,versus Comparative Examples A-D (only 94.5% for Comparative Example Eand well below 80% for Comparative Examples A-D. Importantly, thedisclosed webs demonstrated superior performance over other metals,e.g., copper in Comparative Example E, (99.98+ for Examples 1-6 versusonly 94.5% for Comparative Example E).

Also, the disclosed webs demonstrated a log reduction of well over 2,e.g., greater than 3.5 in most cases. In contrast, Comparative ExamplesA-E, including Comparative Example E, which employed a copper compoundas the antimicrobial agent, demonstrated log reductions less than 1.5,e.g., less than 1.0 in most cases.

These Examples and Comparative Examples demonstrate the criticality ofthe disclosed zinc compound (optionally in the disclosed amounts) versusother antimicrobial agents and versus control samples.

Examples 7 and 8 and Comparative Examples F and G

Nonwoven webs were made using the process described above, with zincoxide added as a masterbatch. The properties and performancecharacteristics of several specific samples are shown in Table 2a.

TABLE 2a Precursor Compositions Average Zn Fiber Basis Zinc amount,Product diameter, weight, Sample compound ppm RV (microns) (gsm) TDI ODI7 Zinc oxide 204 22.2 0.5017 6.75 N/A N/A 8 Zinc oxide 204 22.5 0.57324.25 N/A N/A 9 Zinc oxide 325 23.3 0.5097 12.20 3034 137 Mean Mean poreAir pore size size Filtration permeability diameter pressure EfficiencySample (CFM/ft²) (microns) (PSI) (%) 7 97.98 7.647 0.888 26.37 8 159.807.742 0.892 26.06 9 38.32 6.380 1.056 56.83

Comparative Examples F and G were prepared similarly, but with no zinccompound.

The webs were tested for antimicrobial efficacy (according toISO20743-13:2013). The results are shown in Table 2b.

TABLE 2b Test Results Staphylococcus aureus Klebsiella Pneumoniae Logreduction % Reduction Log reduction % Reduction Color Sample (after 24hours) (after 24 hours) (after 24 hours) (after 24 hours) change 7 4.199.9906 6.1 99.9999 no F 0.3 43.6842 3.7 99.9802 yes 9 5.2 99.9993 6.199.9999 no G 0.1 15.7894 2.6 99.7467 yes

As shown in Table 2b, the webs that comprised the disclosed amounts ofzinc (Examples 7 and 9), demonstrated a surprisingly high reduction(after 24 hours) of both Staphylococcus aureus and Klebsiellapneumoniae, e.g., reduction greater than 99.990% in all cases. Incontrast, Comparative examples F and G, which employed no zinc compound(or elemental zinc) demonstrated reduction less than 50% forStaphylococcus aureus and less than 99.99% for Klebsiella pneumoniae.

In particular, the webs demonstrated particularly good reduction ofKlebsiella pneumoniae, e.g., at least 99.9999%, versus ComparativeExamples F and G (only 99.9802% for Comparative Example F and 99.7467for Comparative Example G.

As shown in Table 2b, for Klebsiella pneumoniae, the disclosed websdemonstrated a log reduction of well over 3.7, e.g., greater than 4 orgreater than 5. In contrast, Comparative Examples F and G, demonstratedlog reductions less than 4.

The performance of Staphylococcus aureus was also unexpectedly good. Thewebs demonstrated reduction of Staphylococcus aureus of at least99.990%, versus Comparative Examples F and G (only 43.68% forComparative Example F and well below 25% for Comparative Example G).

Also, the disclosed webs demonstrated a log reduction of over 3.5, e.g.,greater than 4. In contrast, Comparative Examples F and G demonstratedlog reductions less than 1.5, e.g., less than 1.0 in most cases.

Examples 1-4 and 6 and Comparative Examples a and C (Die PressureReduction)

In addition to the antimicrobial benefits, use of the disclosed amountof zinc has been shown to unexpectedly contribute to processefficiencies, e.g., reductions in die pressure and/or RV improvements.

The precursor polyamide compositions of Examples 1-4 and 6 andComparative Examples A and C were melt blown into webs as describedabove. The die pressures that were used are shown in Table 3. Theremaining process parameters were kept essentially constant, with SampleA having only a slightly higher throughput.

TABLE 3 Die Pressure and RV Sample Die Pressure, psig RV A 605 n/a C 27230.2 1 235 19.4 2 186 18.3 3 140 17.3 4 127 15.6 6 122 16.3

As shown, the use of the disclosed compositions allowed for significantreductions in die pressures and/or RV, e.g., less than 272 psig (toachieve webs having the same or similar characteristics. This is asignificant production advantage because the lower die pressures maycontribute to elimination or reduction of fiber formation interruptions.In some cases, higher die pressures, e.g., greater than 272 psig werefound to allow more fiber formation interruptions, which is detrimentalto web quality. Fiber formation interruptions create defects in the web,which is detrimental for many properties, such as filtration efficiencyand water repellency performance. As shown, the Comparative Examples Aand C were produced at higher die pressures, e.g., 272 psig and 605psig. Webs having the same or similar characteristics were thus achievedusing these higher die pressures. And the higher die pressures are knownto contribute to other defects, e.g., fiber interruptions. Using thedisclosed compositions with the zinc content allows the processes toachieve lower die pressures at higher throughputs, which increases theproduction rates and productivity of the process.

Examples 10 and 11 and Comparative Examples H-M (Die Pressure Reduction)

Precursor polyamide compositions of Examples 10 and 11 and ComparativeExamples H-M were prepared, as shown in Table 4. Examples 10 and 11 wereprepared using the process described above, with zinc stearate as thezinc compound. Comparative Examples H-M were prepared similarly, butwithout zinc compound.

These precursor polyamide compositions were melt blown into webs asdescribed above. The die pressures that were used are also shown inTable 4. The remaining process parameters were kept essentiallyconstant.

TABLE 4 Precursor Compositions and Die Pressure Sample Zn compound Znamount, ppm Die Pressure, psig H — 0 371 I — 0 260 J — 0 371 K — 0 371 L— 0 260 M — 0 501 10 Zn Stearate 3000 153 11 Zn Stearate 310 184

As shown, the use of the disclosed formulations allowed for significantreductions in die pressures, e.g., less than 260 psig (to achieve webshaving the same or similar characteristics. Comparative Examples H-Mwere produced at higher die pressures, e.g., 260 psig or higher, in mostcases well over 350 psig. Webs having the same or similarcharacteristics were thus achieved using these higher die pressures.

EMBODIMENTS

The following embodiments are contemplated. All combinations of featuresand embodiments are contemplated.

Embodiment 1

A nonwoven polyamide composition having permanent antimicrobialproperties comprising: a nonwoven polyamide having an average fiberdiameter of less than 25 microns; less than 2000 ppm zinc dispersedwithin the polyamide; and less than 2000 ppm phosphorus; wherein theweight ratio of the zinc to the phosphorus: is at least 1.3:1; or lessthan 0.64:1.

Embodiment 2

An embodiment of embodiment 1, wherein the weight ratio of the zinc tothe phosphorus is at least 2:1.

Embodiment 3

An embodiment of any one of embodiments 1 and 2, wherein the relativeviscosity of the polyamide composition ranges from 10 to 100, e.g., from20 to 100.

Embodiment 4

An embodiment of any one of embodiments 1-3, wherein the polyamidecomposition comprises less than 500 ppm of zinc.

Embodiment 5

An embodiment of any one of embodiments 1-4, wherein the polyamidecomposition comprises a delusterant including at least a portion of thephosphorus.

Embodiment 6

An embodiment of any one of embodiments 1-5, wherein the polyamidecomposition comprises no phosphorus.

Embodiment 7

An embodiment of any one of embodiments 1-6, wherein the zinc isprovided via a zinc compound comprising zinc oxide, zinc acetate, zincammonium carbonate, zinc ammonium adipate, zinc stearate, zinc phenylphosphinic acid, zinc pyrithione and/or combinations thereof.

Embodiment 8

An embodiment of embodiment 7, wherein the zinc compound is not zincphenyl phosphinate and/or zinc phenyl phosphonate.

Embodiment 9

An embodiment of any one of embodiments 1-8, wherein the phosphorus isprovided via a phosphorus compound comprising phosphoric acid, benzenephosphinic acid, benzene phosphonic acid, manganese hypophosphite,sodium hypophosphite, monosodium phosphate, hypophosphorous acid,phosphorous acid, and/or combinations thereof.

Embodiment 10

An embodiment of any one of embodiments 1-9, wherein the polyamidecomposition comprises less than 500 ppm of zinc, wherein the polymerresin composition comprises a delusterant including at least a portionof the phosphorus, and wherein the polymer resin composition inhibitsgreater than 90% growth of Staphylococcus Aureus as measured by ISO20743-13.

Embodiment 11

An embodiment of any one of embodiments 1-10, wherein the polyamidecomprises a nylon, wherein the zinc is provided via zinc oxide and/orzinc pyrithione, and wherein the relative viscosity of the polyamidecomposition ranges from 10 to 100, e.g., from 20 to 100.

Embodiment 12

An embodiment of any one of embodiments 1-10, wherein the polyamidecomprises nylon-6,6, wherein the zinc is provided via zinc oxide,wherein the weight ratio of zinc to phosphorus is at least 2:1, andwherein the polyamide composition inhibits greater than 95% growth ofStaphylococcus Aureus as measured by ISO 20743-13.

Embodiment 13

An embodiment of any one of embodiments 1-12, further comprising one ormore additional antimicrobial agents comprising silver, tin, copper, andgold, and alloys, oxides, and/or combinations thereof.

Embodiment 14

An embodiment of any one of embodiments 1-13, wherein the melt point ofthe nonwoven is 225° C. or greater.

Embodiment 15

An embodiment of any one of embodiments 1-14, wherein the nonwovenpolyamide is melt spun, spunbonded, electrospun, solution spun, orcentrifugally spun.

Embodiment 16

An embodiment of any one of embodiments 1-15, wherein the average fiberdiameter of the nonwoven polyamide is 1000 nanometers or less.

Embodiment 17

An embodiment of embodiment 16, wherein no more than 20% of the fibershave a diameter of greater than 700 nanometers.

Embodiment 18

An embodiment of any one of embodiments 1-17, wherein the polyamidecomprises nylon 66 or nylon 6/66.

Embodiment 19

An embodiment of any one of embodiments 1-18, wherein the polyamidecomprises a high temperature nylon.

Embodiment 20

An embodiment of any one of embodiments 1-19, wherein the polyamidecomprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T, N11, and/orN12, wherein “N” means Nylon.

Embodiment 21

An embodiment of any one of embodiments 1-20, wherein the nonwovenpolyamide has an Air Permeability Value of less than 600 CFM/ft².

Embodiment 22

An embodiment of any one of embodiments 1-21, wherein the nonwovenpolyamide has a basis weight of 200 GSM or less.

Embodiment 23

An antimicrobial fiber having permanent antimicrobial propertiescomprising: a nonwoven polyamide having an average fiber diameter ofless than 25 microns; less than 2000 ppm zinc dispersed within thepolymer; and less than 2000 ppm phosphorus.

Embodiment 24

An embodiment of embodiment 23, wherein the weight ratio of zinc tophosphorus is: at least 1.3:1; or less than 0.64:1.

Embodiment 25

An embodiment of any one of embodiments 23 or 24, wherein the weightratio of the zinc to the phosphorus is at least 2:1.

Embodiment 26

An embodiment of any one of embodiments 23-25, wherein the fibers havean average diameter less than 20 microns.

Embodiment 27

An embodiment of any one of embodiments 23-26, wherein the polymercomprises less than 2000 ppm zinc.

Embodiment 28

An embodiment of any one of embodiments 23-27, wherein the polymercomprises a delusterant including at least a portion of the phosphorus.

Embodiment 29

An embodiment of any one of embodiments 23-28, wherein the antimicrobialfiber has a zinc retention greater than 70% as measured by a dye bathtest.

Embodiment 30

An embodiment of any one of embodiments 23-29, wherein the zinc is azinc compound comprising zinc oxide, zinc acetate, zinc ammoniumcarbonate, zinc ammonium adipate, zinc stearate, zinc phenyl phosphinicacid, zinc pyrithione and/or combinations thereof.

Embodiment 31

An embodiment of any one of embodiments 23-30, wherein the phosphorus isa phosphorus compound comprising phosphoric acid, benzene phosphinicacid, benzene phosphonic acid, manganese hypophosphite, sodiumhypophosphite, monosodium phosphate, hypophosphorous acid, phosphorousacid, and/or combinations thereof.

Embodiment 32

An embodiment of any one of embodiments 23-31, wherein the polyamidecomprises less than 500 ppm of zinc, wherein the polymer comprises adelusterant including at least a portion of the phosphorus, and whereinthe antimicrobial fiber inhibits greater than 90% growth ofStaphylococcus Aureus as measured by ISO 20743-13.

Embodiment 33

An embodiment of any one of embodiments 23-32, wherein the polyamidecomprises nylon, wherein the zinc is provided in the form of zinc oxideand/or zinc pyrithione, wherein the relative viscosity of the polymerresin composition ranges from 10 to 100, e.g., from 20 to 100, andwherein the antimicrobial fiber has a zinc retention greater than 80% asmeasured by a dye bath test, and wherein the fibers have an averagediameter less than 18 microns.

Embodiment 34

An embodiment of any one of embodiments 23-33, wherein the polyamidecomprises nylon-6,6, wherein the zinc is provided in the form of zincoxide, wherein the weight ratio of zinc to phosphorus is at least 2:1,wherein the antimicrobial fiber inhibits greater than 95% growth ofStaphylococcus Aureus as measured by ISO 20743-13, wherein theantimicrobial fiber has a zinc retention greater than 90% as measured bya dye bath test, and wherein the antimicrobial fibers have an averagediameter less than 10 microns.

Embodiment 35

An embodiment of any one of embodiments 23-34, wherein the polymerfurther comprises one or more additional antimicrobial agents comprisingsilver, tin, copper, and gold, and alloys, oxides, and/or combinationsthereof.

Embodiment 36

An embodiment of any one of embodiments 23-35, wherein the melt point ofthe nonwoven is 225° C. or greater.

Embodiment 37

An embodiment of any one of embodiments 23-36, wherein the nonwovenpolyamide is melt spun, spunbonded, electrospun, solution spun, orcentrifugally spun.

Embodiment 38

An embodiment of any one of embodiments 23-37, wherein the average fiberdiameter of the nonwoven polyamide is 1000 nanometers or less.

Embodiment 39

An embodiment of embodiment 38, wherein no more than 20% of the fibershave a diameter of greater than 700 nanometers.

Embodiment 40

An embodiment of any one of embodiments 23-39, wherein the polyamidecomprises nylon 66 or nylon 6/66.

Embodiment 41

An embodiment of any one of embodiments 23-40, wherein the polyamidecomprises a high temperature nylon.

Embodiment 42

An embodiment of any one of embodiments 23-41, wherein the polyamidecomprises N6, N66, N6T/66, N612, N6/66, N6I/66, N66/6I/6T, N11, and/orN12, wherein “N” means Nylon.

Embodiment 43

An embodiment of any one of embodiments 23-42, wherein the nonwovenpolyamide has an Air Permeability Value of less than 600 CFM/ft².

Embodiment 44

An embodiment of any one of embodiments 23-43, wherein the nonwovenpolyamide has a basis weight of 200 GSM or less.

Embodiment 45

A process for preparing an antimicrobial nonwoven polyamides havingpermanent antimicrobial properties, the process comprising: preparing anaqueous monomer solution forming a polyamide; adding less than 2000 ppmzinc dispersed within the aqueous monomer solution; adding less than2000 ppm phosphorus; polymerizing the aqueous monomer solution to formthe polyamide; spinning the polyamide to form antimicrobial polyamidefibers; and forming the antimicrobial polyamide fibers intoantimicrobial nonwoven polyamides having a fiber diameter of less than25 microns; wherein the weight ratio of zinc to phosphorus is: at least1.3:1 or less than 0.64:1.

Embodiment 46

An embodiment of embodiments 45, wherein the polymer comprises less than2000 ppm zinc.

Embodiment 47

An embodiment of any one of embodiments 45 or 46, wherein theantimicrobial fiber has a zinc retention greater than 70% as measured bya dye bath test.

Embodiment 48

An embodiment of any one of embodiments 45-47, wherein the step ofadding phosphorus comprises adding a delusterant including at least aportion of the phosphorus.

Embodiment 49

An embodiment of any one of embodiments 45-48, wherein the polyamide ismelt spun by way of melt blowing through a die into a high velocitygaseous stream.

Embodiment 50

An embodiment of any one of embodiments 45-49, wherein the polyamide ismelt spun by 2-phase propellant-gas spinning, including extruding thepolyamide composition in liquid form with pressurized gas through afiber-forming channel.

Embodiment 51

An embodiment of any one of embodiments 45-50, wherein the nonwoven isformed by collecting the fibers on a moving belt.

Embodiment 52

An embodiment of any one of embodiments 45-51, wherein the relativeviscosity of the polyamide in the nonwoven is reduced as compared to thepolyamide prior to spinning and forming the nonwoven.

Embodiment 53

An embodiment of any one of embodiments 45-52, wherein the relativeviscosity of the polyamide in the nonwoven is the same or increased ascompared to the polyamide prior to spinning and forming the nonwoven.

Embodiment 54

An embodiment of any one of embodiments 45-53, wherein the nonwovencomprises a nylon 66 polyamide which is melt spun and formed into saidnonwoven, wherein the nonwoven has a TDI of at least 20 ppm and an ODIof at least 1 ppm.

Embodiment 55

An embodiment of any one of embodiments 45-54, wherein the nonwovencomprises a nylon 66 polyamide which is melt spun into fibers and formedinto said nonwoven, wherein no more than 20% of the fibers have adiameter of greater than 25 microns.

Embodiment 56

An embodiment of any one of embodiments 45-49, wherein the polyamide ismelt spun, spunbonded, electrospun, solution spun, or centrifugallyspun.

Embodiment 57

A nonwoven polyamide structure having antimicrobial propertiescomprising: nonwoven polyamide fibers comprising less than 4000 ppm zincdispersed within the nonwoven polyamide fibers; and less than 2000 ppmphosphorus; wherein the fibers have an average fiber diameter of lessthan 25 microns; and wherein the polyamide structure demonstrates aStaphylococcus Aureus reduction of at least 90%, as measured by ISO20743-13.

Embodiment 58

An embodiment of embodiment 57, wherein the weight ratio of the zinc tothe phosphorus is at least 1.3:1; or less than 0.64:1.

Embodiment 59

An embodiment of any one of embodiments 57 or 58, wherein the relativeviscosity of the polyamide composition is less than 100.

Embodiment 60

An embodiment of any one of embodiments 57-59, wherein the polyamidecomposition comprises less than 3100 ppm of zinc, wherein the polyamidecomposition comprises a delusterant including at least a portion of thephosphorus, and wherein the polyamide demonstrates a StaphylococcusAureus reduction of at least 90%, as measured by ISO 20743-13.

Embodiment 61

An embodiment of any one of embodiments 57-60, wherein the nonwovenpolyamide is melt spun, spunbonded, electrospun, solution spun, orcentrifugally spun.

Embodiment 62

An embodiment of any one of embodiments 57-61, wherein no more than 20%of the fibers have a diameter of greater than 700 nanometers.

Embodiment 63

An embodiment of any one of embodiments 57-62, wherein the polyamidecomprises nylon 66 or nylon 6/66.

Embodiment 64

Antimicrobial fibers having antimicrobial properties comprising lessthan 4000 ppm zinc dispersed within the nonwoven polyamide fibers; lessthan 2000 ppm phosphorus, wherein the fibers have an average fiberdiameter of less than 25 microns; and wherein the polyamide structuredemonstrates a Staphylococcus Aureus reduction of at least 90%, asmeasured by ISO 20743-13.

Embodiment 65

An embodiment of embodiment 64, wherein the weight ratio of zinc tophosphorus is: at least 1.3:1; or less than 0.64:1.

Embodiment 66

An embodiment of any one of embodiment 64 or 65, wherein the fibers havean average diameter less than 20 microns.

Embodiment 67

An embodiment of any one of embodiments 64-66, wherein the nonwovenpolyamide comprises less than 3100 ppm of zinc.

Embodiment 68

An embodiment of any one of embodiments 64-67, wherein the antimicrobialfibers have a zinc retention greater than 70% as measured by a dye bathtest.

Embodiment 69

An embodiment of any one of embodiments 64-68, wherein the nonwovenpolyamide comprises less than 3200 ppm of zinc, wherein the polymercomprises a delusterant including at least a portion of the phosphorus,and wherein the antimicrobial fibers demonstrates a StaphylococcusAureus reduction of at least 90%, as measured by ISO 20743-13.

Embodiment 70

An embodiment of any one of embodiments 64-69, wherein the nonwovenpolyamide is melt spun, spunbonded, electrospun, solution spun, orcentrifugally spun.

Embodiment 71

An embodiment of any one of embodiments 64-70, wherein the polyamidecomprises nylon 66 or nylon 6/66.

Embodiment 72

A process for preparing an antimicrobial nonwoven polyamide structurehaving permanent antimicrobial properties, the process comprising:preparing precursor polyamide optionally comprising an aqueous monomersolution; dispersing less than 4000 ppm zinc within the precursorpolyamide; dispersing less than 2000 ppm phosphorus within the precursorpolyamide; polymerizing the precursor polyamide to form a polyamidecomposition; spinning the polyamide composition to form antimicrobialpolyamide fibers; and forming the antimicrobial polyamide fibers intothe antimicrobial nonwoven structure having a fiber diameter of lessthan 25 microns.

Embodiment 73

An embodiment of embodiment 72, wherein the antimicrobial nonwovenpolyamides have a zinc retention greater than 70% as measured by a dyebath test.

Embodiment 74

An embodiment of any one of embodiment 72 or 73, wherein the weightratio of zinc to phosphorus is: at least 1.3:1; or less than 0.64:1.

Embodiment 75

An embodiment of any one of embodiments 72-74, wherein the polyamide ismelt spun by way of melt blowing through a die into a high velocitygaseous stream.

Embodiment 76

An embodiment of any one of embodiments 72-75, wherein the nonwovencomprises a nylon 66 polyamide which is melt spun into fibers and formedinto said nonwoven, wherein no more than 20% of the fibers have adiameter of greater than 25 microns.

Embodiment 77

An embodiment of any one of embodiments 72-76, wherein the polyamide ismelt spun, spunbonded, electrospun, solution spun, or centrifugallyspun.

Embodiment 78

A nonwoven polyamide structure having antimicrobial propertiescomprising: nonwoven polyamide fibers having an average fiber diameterof less than 25 microns; less than 4000 ppm zinc dispersed within thenonwoven polyamide fibers; wherein the polyamide compositiondemonstrates a Staphylococcus Aureus reduction of at least 90%, asmeasured by ISO 20743-13.

Embodiment 79

A process for preparing an antimicrobial nonwoven polyamide structurehaving antimicrobial properties, the process comprising: preparing aformulation comprising a polyamide, less than 4000 ppm zinc dispersedwithin the polyamide; and less than 2000 ppm phosphorus dispersed withinthe polyamide; spinning the formulation to form antimicrobial polyamidefibers having a fiber diameter of less than 25 microns; and forming theantimicrobial polyamide fibers into antimicrobial nonwoven polyamidestructure; wherein the fibers were spun using a die pressure less than275 psig

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that embodiments of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.

We claim:
 1. A nonwoven polyamide structure having antimicrobialproperties comprising: nonwoven polyamide fibers comprising a polyamidecomposition comprising: less than 4000 ppm zinc dispersed within thenonwoven polyamide fibers; and less than 2000 ppm phosphorus, whereinthe fibers have an average fiber diameter of less than 20 microns;wherein the zinc is provided via a zinc compound and the phosphorus isprovided via a phosphorus compound different from the zinc compound; andwherein the polyamide structure demonstrates a Staphylococcus Aureusreduction of at least 90%, as measured by ISO 20743-13.
 2. The nonwovenpolyamide structure of claim 1, wherein the weight ratio of the zinc tothe phosphorus is at least 1.3:1; or less than 0.64:1.
 3. The nonwovenpolyamide structure of claim 1, wherein the relative viscosity of thepolyamide composition is less than
 100. 4. The nonwoven polyamidestructure of claim 1, wherein the polyamide composition comprises lessthan 3100 ppm of zinc, wherein the polyamide composition comprises adelusterant including at least a portion of the phosphorus, and whereinthe polyamide demonstrates a Staphylococcus Aureus reduction of at least90%, as measured by ISO 20743-13.
 5. The nonwoven polyamide structure ofclaim 1, wherein no more than 20% of the fibers have a diameter ofgreater than 700 nanometers.
 6. The nonwoven polyamide structure ofclaim 1, wherein the polyamide comprises nylon 66 or nylon 6/66. 7.Antimicrobial fibers having antimicrobial properties comprising: apolymer; less than 4000 ppm zinc dispersed within the polymer; and lessthan 2000 ppm phosphorus, wherein the fibers have an average fiberdiameter of less than 20 microns; wherein the zinc is provided via azinc compound and the phosphorus is provided via a phosphorus compounddifferent from the zinc compound; and wherein the antimicrobial fibersdemonstrate a Staphylococcus Aureus reduction of at least 90%, asmeasured by ISO 20743-13.
 8. The antimicrobial fibers of claim 7,wherein the weight ratio of zinc to phosphorus is: at least 1.3:1; orless than 0.64:1.
 9. The antimicrobial fibers of claim 7, wherein theantimicrobial fibers comprise less than 3100 ppm of zinc.
 10. Theantimicrobial fibers of claim 7, wherein the antimicrobial fibers have azinc retention greater than 70% as measured by a dye bath test.
 11. Theantimicrobial fibers of claim 7, wherein the antimicrobial fiberscomprise less than 3200 ppm of zinc, wherein the antimicrobial fiberscomprise a delusterant including at least a portion of the phosphorus,and wherein the antimicrobial fibers demonstrates a StaphylococcusAureus reduction of at least 90%, as measured by ISO 20743-13.
 12. Theantimicrobial fibers of claim 7, wherein the antimicrobial fiberscomprise nylon 66 or nylon 6/66.
 13. A process for preparing anantimicrobial nonwoven polyamide structure having permanentantimicrobial properties, the process comprising: preparing precursorpolyamide comprising an aqueous monomer solution; dispersing less than4000 ppm zinc within the precursor polyamide; dispersing less than 2000ppm phosphorus within the precursor polyamide; wherein the zinc isprovided via a zinc compound and the phosphorus is provided via aphosphorus compound different from the zinc compound; polymerizing theprecursor polyamide to form a polyamide composition; spinning thepolyamide composition to form antimicrobial polyamide fibers; andforming the antimicrobial polyamide fibers into the antimicrobialnonwoven structure having a fiber diameter of less than 20 microns; andwherein the polyamide structure demonstrates a Staphylococcus Aureusreduction of at least 90%, as measured by ISO 20743-13.
 14. The processof claim 13, wherein the antimicrobial nonwoven polyamides have a zincretention greater than 70% as measured by a dye bath test.
 15. Theprocess of claim 13, wherein the weight ratio of zinc to phosphorus is:at least 1.3:1 or less than 0.64:1.
 16. The process of claim 13, whereinthe polyamide is melt spun by way of melt blowing through a die into ahigh velocity gaseous stream.
 17. A process for preparing anantimicrobial nonwoven polyamide structure having antimicrobialproperties, the process comprising: preparing a formulation comprising apolyamide, less than 4000 ppm zinc dispersed within the polyamide; andless than 2000 ppm phosphorus dispersed within the polyamide, whereinthe zinc is provided via a zinc compound and the phosphorus is providedvia a phosphorus compound different from the zinc compound; spinning theformulation to form antimicrobial polyamide fibers having a fiberdiameter c less than 20 microns; and forming the antimicrobial polyamidefibers into antimicrobial nonwoven polyamide structure; wherein thefibers were spun using a die pressure less than 275 psig; and whereinthe polyamide structure demonstrates a Staphylococcus Aureus reductionof at least 90%, as measured by ISO 20743-13.